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Anatomy_Gray. Initial treatment is aimed at reducing the inflammation and removing any repetitive insults that produce the symptoms. If this does not lead to improvement, nerve conduction studies will be necessary to confirm nerve entrapment, which may require surgical decompression of the flexor retinaculum. In the clinic The palmar fascia can become abnormally thickened in certain individuals, causing the fingers to progressively develop a fixed flexion position. This results in loss of dexterity and function, and in severe cases requires surgical removal of the abnormal tissue. In the clinic The anatomical snuffbox is an important clinical region. When the hand is in ulnar deviation, the scaphoid becomes palpable within the snuffbox. This position enables the physician to palpate the bone to assess for a fracture. The pulse of the radial artery can also be felt in the snuffbox. In the clinic


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Anatomy_Gray. In the clinic De Quervain’s syndrome is an inflammatory disorder that occurs within the first dorsal extensor compartment and involves the extensor pollicis brevis tendon and abductor pollicis longus tendon and their common tendon sheath (Fig. 7.102). Patients typically present with significant wrist pain preventing appropriate flexion/extension and abduction of the thumb. The cause of this disorder is often overuse. For example, the syndrome is common in young mothers who are constantly lifting young children. Other causes include inflammatory disorders such as rheumatoid arthritis. In the clinic


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Anatomy_Gray. In the clinic Tenosynovitis is inflammation of a tendon and its sheath. The condition may be caused by overuse; however, it can also be associated with other disorders such as rheumatoid arthritis and connective tissue pathologies. If the inflammation becomes severe and ensuing fibrosis occurs, the tendon will not run smoothly within the tendon sheath, and typically within the fingers the tendon may stick or require excess force to fully extend and flex, producing a “triggering” phenomenon. In the clinic Trigger finger is a common disorder of late childhood and adulthood and is typically characterized by catching or snapping and occasionally locking of the flexor tendon(s) in the hand. Trigger finger can be associated with significant dysfunction and pain. The triggering is usually related to fibrosis and tightening of the flexor tendon sheath at the level of the metacarpophalangeal joint. In the clinic


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Anatomy_Gray. In the clinic To test for adequate anastomoses between the radial and ulnar arteries, compress both the radial and ulnar arteries at the wrist, then release pressure from one or the other, and determine the filling pattern of the hand. If there is little connection between the deep and superficial palmar arteries, only the thumb and lateral side of the index finger will fill with blood (become red) when pressure on the radial artery alone is released. In the clinic


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Anatomy_Gray. In the clinic In many patients, venous access is necessary for obtaining blood for laboratory testing and administering fluid and intravenous drugs. The ideal sites for venous access are typically in the cubital fossa and in the cephalic vein adjacent to the anatomical snuffbox. The veins are simply distended by use of a tourniquet. A tourniquet should be applied enough to allow the veins to become prominent. For straightforward blood tests the antecubital vein is usually the preferred site, and although it may not always be visible, it is easily palpated. The cephalic vein is generally the preferred site for a short-term intravenous cannula. In the clinic The ulnar nerve is most commonly injured at two sites: the elbow and the wrist. At the elbow, the nerve lies posterior to the medial epicondyle. At the wrist, the ulnar nerve passes superficial to the flexor retinaculum and lies lateral to the pisiform bone.


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Anatomy_Gray. At the elbow, the nerve lies posterior to the medial epicondyle. At the wrist, the ulnar nerve passes superficial to the flexor retinaculum and lies lateral to the pisiform bone. Ulnar nerve lesions are characterized by “clawing” of the hand, in which the metacarpophalangeal joints of the fingers are hyperextended and the interphalangeal joints are flexed because the function of most of the intrinsic muscles of the hand is lost (Fig. 7.114). Clawing is most pronounced in the medial fingers because the function of all intrinsic muscles of these digits is lost while in the lateral two digits, the lumbricals are innervated by the median nerve. Function of the adductor pollicis muscle is also lost.


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Anatomy_Gray. In lesions of the ulnar nerve at the elbow, function of the flexor carpi ulnaris muscle and flexor digitorum profundus to the medial two digits is lost as well. Clawing of the hand, particularly of the little and ring fingers, is worse with lesions of the ulnar nerve at the wrist than at the elbow because interruption of the nerve at the elbow paralyzes the ulnar half of the flexor digitorum profundus, which leads to lack of flexion at the distal interphalangeal joints in these fingers. Ulnar nerve lesions at the elbow and wrist result in impaired sensory innervation on the palmar aspect of the medial one and one-half digits. Damage to the ulnar nerve at the wrist or at a site proximal to the wrist can be distinguished by evaluating the status of function of the dorsal branch (cutaneous) of the ulnar nerve, which originates in distal regions of the forearm. This branch innervates skin over the dorsal surface of the hand on the medial side. In the clinic


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Anatomy_Gray. In the clinic Around the elbow joint the radial nerve divides into its two terminal branches—the superficial branch and the deep branch. The most common radial nerve injury is damage to the nerve in the radial groove of the humerus, which produces a global paralysis of the muscles of the posterior compartment, resulting in wrist drop. Radial nerve damage can result from fracture of the shaft of the humerus as the radial nerve spirals around in the radial groove. The typical injury produces reduction of sensation in the cutaneous distribution, predominantly over the posterior aspect of the hand. Severing the posterior interosseous nerve (continuation of deep branch of radial nerve) may paralyze the muscles of the posterior compartment of the forearm, but the nerve supply is variable. Typically, the patient may not be able to extend the fingers.


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Anatomy_Gray. The distal branches of the superficial branch of the radial nerve can be readily palpated as “cords” passing over the tendon of the extensor pollicis longus in the anatomical snuffbox. Damage to these branches is of little consequence because they supply only a small area of skin. A 57-year-old woman underwent a right mastectomy for a breast cancer. The surgical note reported that all of the breast tissue had been removed, including the axillary process. In addition, the surgeon had dissected all lymph nodes within the axilla with their surrounding fat. The patient made an uneventful recovery. At the first follow-up appointment, the patient’s husband told the surgeon that she had now developed a bony “spike” on her back. The surgeon was intrigued and asked the patient to reveal this spike. At examination, the spike was the inferior angle of the scapula, which appeared to be sticking out posteriorly (“winged”). Raising the arms accentuated this structure.


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Anatomy_Gray. The medial border of the scapula was accentuated and it was noted that there was some loss of bulk of the serratus anterior muscle, which attaches to the tip of the scapula. The nerve to this muscle was damaged. During the surgery on the axilla, the long thoracic nerve was damaged as it passed down the lateral thoracic wall on the external surface of the serratus anterior, just deep to the skin and subcutaneous fascia. Because the nerve was transected, it is unlikely that the patient will improve, but she was happy that she had an adequate explanation for the spike. A 25-year-old woman was involved in a motor vehicle accident and thrown from her motorcycle. When she was admitted to the emergency room, she was unconscious. A series of tests and investigations were performed, one of which included chest radiography. The attending physician noted a complex fracture of the first rib on the left. Many important structures that supply the upper limb pass over rib I.


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Anatomy_Gray. Many important structures that supply the upper limb pass over rib I. It is important to test the nerves that supply the arm and hand, although this is extremely difficult to do in an unconscious patient. However, some muscle reflexes can be determined using a tendon hammer. Also, it may be possible to test for pain reflexes in patients with altered consciousness levels. Palpation of the axillary artery, brachial artery, radial artery, and ulnar artery pulses is necessary because a fracture of the first rib can sever and denude the subclavian artery, which passes over it. A chest drain was immediately inserted because the lung had collapsed. The fractured first rib had damaged the visceral and parietal pleurae, allowing air from a torn lung to escape into the pleural cavity. The lung collapsed, and the pleural cavity filled with air, which impaired lung function. A tube was inserted between the ribs, and the air was sucked out to re-inflate the lung.


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Anatomy_Gray. A tube was inserted between the ribs, and the air was sucked out to re-inflate the lung. The first rib is a deep structure at the base of the neck. It is not uncommon for ribs to be broken after minor injuries, including sports injuries. However, rib I, which lies at the base of the neck, is surrounded by muscles and soft tissues that provide it with considerable protection. Therefore a patient with a fracture of the first rib has undoubtedly been subjected to a considerable force, which usually occurs in a deceleration injury. Other injuries should always be sought and the patient should be managed with a high level of concern for deep neck and mediastinal injuries. A resident was asked to carry out a clinical assessment of a patient’s hand. He examined the following:


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Anatomy_Gray. A resident was asked to carry out a clinical assessment of a patient’s hand. He examined the following: The musculoskeletal system includes the bones, joints, muscles, and tendons. The resident looked for abnormalities and muscle wasting. Knowing which areas are wasted identifies the nerve that supplies them. She palpated the individual bones and palpated the scaphoid with the wrist in ulnar deviation. She examined the movement of joints because they may be restricted by joint disease or inability of muscular contraction. Palpation of both radial and ulnar pulses is necessary. The resident looked for capillary return to assess how well the hand was perfused. Examination of the nerves The three main nerves to the hand should be tested.


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Anatomy_Gray. Examination of the nerves The three main nerves to the hand should be tested. The median nerve innervates the skin on the palmar aspect of the lateral three and one-half digits, the dorsal aspect of the distal phalanx, half of the middle phalanges of the same fingers, and a variable amount on the radial side of the palm of the hand. Median nerve damage results in wasting of the thenar eminence, absence of abduction of the thumb, and absence of opposition of the thumb. The ulnar nerve innervates the skin of the anterior and posterior surfaces of the little finger and the ulnar side of the ring finger, the skin over the hypothenar eminence, and a similar strip of skin posteriorly. Sometimes the ulnar nerve innervates all the skin of the ring finger and the ulnar side of the middle finger.


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Anatomy_Gray. An ulnar nerve palsy results in wasting of the hypothenar eminence, absent flexion of the distal interphalangeal joints of the little and ring fingers, and absent abduction and adduction of the fingers. Adduction of the thumb also is affected. The radial nerve innervates a small area of skin over the lateral aspect of metacarpal I and the back of the first web space. The radial nerve also produces extension of the wrist and extension of the metacarpophalangeal and interphalangeal joints and of the digits. A very simple examination would include tests for the median nerve by opposition of the thumb, for the ulnar nerve by abduction and adduction of the digits, and for the radial nerve by extension of the wrist and fingers and feeling on the back of the first web space.


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Anatomy_Gray. A 45-year-old man came to his physician complaining of pain and weakness in his right shoulder. The pain began after a fall on his outstretched hand approximately 6 months previously. The patient recalled having some minor shoulder tenderness but no other specific symptoms. He was otherwise fit and well. On examination of the shoulder, there was marked wasting of the muscles in the supraspinous and infraspinous fossae. The patient found initiation of abduction difficult and there was a weakness of lateral rotation of the humerus. The wasted muscles were the supraspinatus and infraspinatus. The cause of the muscle wasting was disuse. Muscle atrophy (wasting) occurs through a variety of disorders. Disuse atrophy is one of the most common causes. Examples of disuse atrophy include the loss of muscle bulk after fracture immobilization in a plaster cast. The opposite effect can also be demonstrated—when muscles are overused they become bulkier (hypertrophy).


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Anatomy_Gray. The supraspinatus and infraspinatus muscles are supplied by the suprascapular nerve (C5, C6), which originates from the superior trunk of the brachial plexus. Given that only these muscles were involved, it is highly likely that the muscle atrophy is caused by denervation. Denervation may result from a direct nerve transection, nerve compression, or a pharmacological effect on the nerve. The typical site for compression of the suprascapular nerve is the suprascapular notch (foramen) on the superior margin of the scapula. The patient’s apparently minor injury damaged the fibrocartilaginous glenoid labrum, which allowed a cyst to form and pass along the superior border of the scapula to the suprascapular notch (foramen), where the cyst compressed the suprascapular nerve. Surgical excision of the damaged glenoid labrum and removal of the cyst improved the patient’s symptoms.


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Anatomy_Gray. Surgical excision of the damaged glenoid labrum and removal of the cyst improved the patient’s symptoms. A surgeon wished to carry out a complex procedure on a patient’s wrist, and asked the anesthesiologist whether the whole arm could be numbed while the patient was awake. Within 20 minutes the anesthesiologist had carried out the procedure after injecting 10 mL of local anesthetic into the axilla. The surgeon went ahead with the operation and the patient did not feel a thing. The anesthetic was injected into the axillary sheath. It would be almost impossible to anesthetize the wrist in the forearm because local anesthetic would have to be placed accurately around the ulnar, median, and radial nerves. Furthermore, all of the cutaneous branches of the forearm would also have to be anesthetized individually, which would take a considerable amount of time and probably produce subtotal anesthesia.


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Anatomy_Gray. The nerves of the upper limb originate from the brachial plexus, which surrounds the axillary artery within the axilla. Importantly, the axillary artery, axillary vein, and brachial plexus lie within the sleeve-like covering of fascia termed the axillary sheath. By injecting the anesthetic into the space enclosed by the axillary sheath, all of the nerves of the brachial plexus were paralyzed. It is possible with a patient’s arm abducted and externally rotated (palm behind the head) to easily palpate the axillary artery and therefore locate the position of the axillary sheath. Once the axillary artery has been identified, a small needle can be placed beside the vessel and local anesthetic can be injected on both sides of it. The local anesthetic tracks along the axillary sheath in this region. The brachial plexus surrounding the axillary artery is therefore completely anesthetized and an effective local anesthetic “block” is achieved.


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Anatomy_Gray. “Could there be any complications?” asks the patient. Potential complications are a direct needle spike of the branches of the brachial plexus, damage to the axillary artery, and inadvertent arterial injection of the local anesthetic. Fortunately, these are rare in skilled hands. A 35-year-old woman comes to her physician complaining of tingling and numbness in the fingertips of the first, second, and third digits (thumb, index, and middle fingers). The symptoms were provoked by arm extension. Local anesthesia was also present around the base of the thenar eminence. The problem was diagnosed as median nerve compression.


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Anatomy_Gray. The problem was diagnosed as median nerve compression. The median nerve is formed from the lateral and medial cords of the brachial plexus anterior to the axillary artery and passes into the arm anterior to the brachial artery. At the level of the elbow joint it sits medial to the brachial artery, both of which are medial to the tendon of the biceps. In the forearm the nerve courses through the anterior compartment and passes deep to the flexor retinaculum. It innervates most of the muscles of the forearm, the thenar muscles, the two lateral lumbricals, and the skin over the palmar surface of the lateral three and one-half digits and over the lateral side of the palm and the middle of the wrist. In this patient, the median nerve initially was believed to be trapped below the flexor retinaculum (carpal tunnel syndrome).


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Anatomy_Gray. In this patient, the median nerve initially was believed to be trapped below the flexor retinaculum (carpal tunnel syndrome). Carpal tunnel syndrome is a common problem in young to middle-aged patients. Typically the nerve becomes compressed within the carpal tunnel. This syndrome may be associated with a number of medical conditions, such as thyroid disease and pregnancy. Occasionally a small ganglion or a tumor situated within the carpal tunnel can also compress the nerve. Other possibilities include tenosynovitis in patients with rheumatoid arthritis.


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Anatomy_Gray. Nerve conduction studies were performed to confirm the clinical findings. Nerve conduction studies are a series of tests that send small electrical impulses along the length of a variety of nerves in order to measure the speed at which the nerve conducts these pulses. The speed of the nerve pulse can be measured and is referred to as the latency. In our patient it was noted that the nerve had normal latency to the elbow joint; however, below the elbow joint there was increased latency. The nerve conduction studies indicated that the compression site was at the elbow joint.


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Anatomy_Gray. The nerve conduction studies indicated that the compression site was at the elbow joint. The clinical findings are not consistent with carpal tunnel syndrome. The clinician should have been alerted to this problem given that the patient experienced numbness over the thenar eminence of the hand. This clue indicates an understanding of the anatomy. Compression of the nerve within the carpal tunnel does not produce this numbness, because the small cutaneous branch that supplies this region is proximal to the flexor retinaculum. The nerve compromise was caused by the ligament of Struthers, which is an embryological remnant of the coracobrachialis muscle. It is an extremely rare finding. Occasionally it may ossify and cross the nerve, artery, and vein to produce compression in arm extension. Although this is very rare and unusual, it illustrates the complex course of the median nerve.


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Anatomy_Gray. After a hard day’s studying, two medical students decided to meet for coffee. The more senior student said to the freshman that he would bet him $50 that he could not lift a matchbook with a finger. The freshman placed $50 on the table and the bet was on. The senior medical student told the freshman to make a fist and place it in a palm-downward position, so that the middle phalanges of the fingers were in direct contact with the bar counter. He was then told to extend his middle finger so that it stuck forward while maintaining the middle phalanges of the index finger, the ring finger, and the little finger on the bar surface. A matchbook was placed on top of the freshman’s middle fingernail and he was told to flip it. He couldn’t. He lost the $50. Extension of the index, middle, ring, and little fingers is performed by the extensor digitorum muscle.


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Anatomy_Gray. Extension of the index, middle, ring, and little fingers is performed by the extensor digitorum muscle. Placing the fist in a palm-down position on the table and pressing the middle phalanges onto the table effectively immobilizes the action of the extensor digitorum. The freshman was therefore unable to elevate his middle finger (which was sticking out). It is important to remember that if this same procedure is carried out leaving the index or little finger free to move, they do. This is because these two digits are extended not only by the extensor digitorum muscle but also by the extensor indicis muscle (index finger) and extensor digiti minimi muscle (little finger). A 70-year-old woman came to an orthopedic surgeon with right shoulder pain and failure to initiate abduction of the shoulder. Further examination revealed loss of muscle bulk in the supraspinous fossa. The supraspinatus muscle was damaged.


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Anatomy_Gray. Abduction of the humerus at the glenohumeral joint is initiated by the supraspinatus muscle. After the shoulder has been abducted to 10°–15°, the deltoid muscle continues the movement. The patient was able to abduct her arm by lowering and tilting the glenohumeral joint inferiorly to enable the deltoid to obtain its mechanical advantage. The loss of muscle bulk in the supraspinous fossa suggested muscle atrophy. Muscle atrophy occurs when a muscle is not used. The orthopedic surgeon thought that there was a tear of the supraspinatus tendon beneath the acromion. If this was so, the muscle would atrophy. The diagnosis was confirmed by ultrasound scan.


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Anatomy_Gray. The diagnosis was confirmed by ultrasound scan. The patient was seated on a stool and her right shoulder was uncovered. The patient’s hand was placed over her right buttock, a position that acts to externally rotate and extend the shoulder, exposing the supraspinatus tendon for ultrasound scan examination. The ultrasound revealed a completely torn tendon with fluid in the subacromial subdeltoid bursa (eFig. 7.128). The patient underwent a surgical repair and made a good recovery. A 35-year-old baseball pitcher came to the clinic with a history of a recurrent dislocation of the shoulder (eFig. 7.129). An MRI scan was performed to assess the shoulder joint prior to any treatment. The MRI demonstrates the anatomical structures in multiple planes, allowing the physician to obtain an overview of the shoulder and to assess any intraarticular or extraarticular structures that may have been damaged and require surgical repair.


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Anatomy_Gray. The MRI demonstrated a divot in the posterosuperior aspect of the humeral head and a small fragment of bone and glenoid labrum that had become separated in the anteroinferior aspect of the glenoid cavity. Shoulder dislocation is not an uncommon problem and may occur as a “once-off” or with repetitive injury may be recurrent. Recurrent dislocations may be bilateral and symmetrical (a memory aid is “torn loose or born loose”).


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Anatomy_Gray. The MRI findings are typical for an anteroinferior dislocation, which is the most common type; moreover the MRI demonstrates the injuries that occur within the joint at the time of dislocation. These injuries include the abutment of the posterosuperior aspect of the humeral head on the anteroinferior aspect of the glenoid cavity. This type of injury, when recurrent, may avulse a small fragment of the glenoid labrum, and in some cases this may attach to a small fragment of bone (the Bankart lesion). When the shoulder is relocated, the integrity of the capsular attachment anteroinferiorly has been disrupted, potentially making the shoulder somewhat prone to further dislocation. An arthroscopic repair was performed.


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Anatomy_Gray. An arthroscopic repair was performed. Arthroscopy of the shoulder is an established method for assessing the shoulder joint. Portals of entry are anterior and posterior and small holes in the capsule are made percutaneously. The shoulder joint is filled with saline, which distends it, allowing the arthroscope to move around the joint and inspect the joint surfaces, including the labrum. The labrum and its bony fragment were reattached and sutured using anchor sutures (somewhat similar to staples). The anterior aspect of the capsule was also tightened. The patient made an uneventful recovery. After the procedure the arm was held in internal rotation and remained adducted. Gentle exercise and physiotherapy were performed and the patient returned to playing baseball. 821.e1 821.e2 Conceptual Overview • Relationship to Other Regions Fig. 7.40, cont’d


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Anatomy_Gray. 821.e1 821.e2 Conceptual Overview • Relationship to Other Regions Fig. 7.40, cont’d Table 7.7 Branches of brachial plexus (parentheses indicate that a spinal segment is a minor component of the nerve or is inconsistently present in the nerve)—cont’d Fig. 7.63, cont’d Fig. 7.66, cont’d Regional Anatomy • Anterior Compartment of the Forearm Regional Anatomy • Anterior Compartment of the Forearm Regional Anatomy • Anterior Compartment of the Forearm Regional Anatomy • Anterior Compartment of the Forearm Regional Anatomy • Posterior Compartment of the Forearm Regional Anatomy • Posterior Compartment of the Forearm Regional Anatomy • Posterior Compartment of the Forearm Regional Anatomy • Posterior Compartment of the Forearm Fig. 7.94, cont’d Surface Anatomy • Visualizing the Axilla and Locating Contents and Related Structures Surface Anatomy • Identifying Tendons and Locating Major Vessels and Nerves in the Distal Forearm


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Anatomy_Gray. Surface Anatomy • Visualizing the Axilla and Locating Contents and Related Structures Surface Anatomy • Identifying Tendons and Locating Major Vessels and Nerves in the Distal Forearm Surface Anatomy • Motor Function of the Median and Ulnar Nerves in the Hand Arrangement of meninges and spaces 865 Anterior triangle of the neck 995 Posterior triangle of the neck 1012 Root of the neck 1019 Gaps in the pharyngeal wall and structures passing through them 1035 Cavity of the larynx 1048 Function of the larynx 1053 Walls, floor, and roof 1065 Multiple nerves innervate the oral cavity 1077 Walls: the cheeks 1080 Anatomical position of the head and major landmarks 1110 Visualizing structures at the CIII/CIV and CVI vertebral levels 1111 How to outline the anterior and posterior triangles of the neck 1112 How to locate the cricothyroid ligament 1113 How to find the thyroid gland 1114 Estimating the position of the middle meningeal artery 1114


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Anatomy_Gray. How to locate the cricothyroid ligament 1113 How to find the thyroid gland 1114 Estimating the position of the middle meningeal artery 1114 Major features of the face 1115 The eye and lacrimal apparatus 1116 The head and neck are anatomically complex areas of the body. The head is composed of a series of compartments, which are formed by bone and soft tissues. They are: the cranial cavity, two ears, two orbits, two nasal cavities, and an oral cavity (Fig. 8.1). The cranial cavity is the largest compartment and contains the brain and associated membranes (meninges). Most of the ear apparatus on each side is contained within one of the bones forming the floor of the cranial cavity. The external parts of the ears extend laterally from these regions.


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Anatomy_Gray. Most of the ear apparatus on each side is contained within one of the bones forming the floor of the cranial cavity. The external parts of the ears extend laterally from these regions. The two orbits contain the eyes. They are cone-shaped chambers immediately inferior to the anterior aspect of the cranial cavity, and the apex of each cone is directed posteromedially. The walls of the orbits are bone, whereas the base of each conical chamber can be opened and closed by the eyelids. The nasal cavities are the upper parts of the respiratory tract and are between the orbits. They have walls, floors, and ceilings, which are predominantly composed of bone and cartilage. The anterior openings to the nasal cavities are nares (nostrils), and the posterior openings are choanae (posterior nasal apertures). Continuous with the nasal cavities are air-filled extensions (paranasal sinuses), which project laterally, superiorly, and posteriorly into surrounding bones.


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Anatomy_Gray. Continuous with the nasal cavities are air-filled extensions (paranasal sinuses), which project laterally, superiorly, and posteriorly into surrounding bones. The largest, the maxillary sinuses, are inferior to the orbits. The oral cavity is inferior to the nasal cavities, and separated from them by the hard and soft palates. The floor of the oral cavity is formed entirely of soft tissues. The anterior opening to the oral cavity is the oral fissure (mouth), and the posterior opening is the oropharyngeal isthmus. Unlike the nares and choanae, which are continuously open, both the oral fissure and oropharyngeal isthmus can be opened and closed by surrounding soft tissues.


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Anatomy_Gray. In addition to the major compartments of the head, two other anatomically defined regions (infratemporal fossa and pterygopalatine fossa) of the head on each side are areas of transition from one compartment of the head to another (Fig. 8.2). The face and scalp also are anatomically defined areas of the head and are related to external surfaces. The infratemporal fossa is an area between the posterior aspect (ramus) of the mandible and a flat region of bone (lateral plate of the pterygoid process) just posterior to the upper jaw (maxilla). This fossa, bounded by bone and soft tissues, is a conduit for one of the major cranial nerves—the mandibular nerve (the mandibular division of the trigeminal nerve [V3]), which passes between the cranial and oral cavities.


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Anatomy_Gray. The pterygopalatine fossa on each side is just posterior to the upper jaw. This small fossa communicates with the cranial cavity, the infratemporal fossa, the orbit, the nasal cavity, and the oral cavity. A major structure passing through the pterygopalatine fossa is the maxillary nerve (the maxillary division of the trigeminal nerve [V2]). The face is the anterior aspect of the head and contains a unique group of muscles that move the skin relative to underlying bone and control the anterior openings to the orbits and oral cavity (Fig. 8.3). The scalp covers the superior, posterior, and lateral regions of the head (Fig. 8.3). The neck extends from the head above to the shoulders and thorax below (Fig. 8.4). Its superior boundary is along the inferior margins of the mandible and bone features on the posterior aspect of the skull. The posterior neck is higher than the anterior neck to connect cervical viscera with the posterior openings of the nasal and oral cavities.


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Anatomy_Gray. The inferior boundary of the neck extends from the top of the sternum, along the clavicle, and onto the adjacent acromion, a bony projection of the scapula. Posteriorly, the inferior limit of the neck is less well defined, but can be approximated by a line between the acromion and the spinous process of vertebra CVII, which is prominent and easily palpable. The inferior border of the neck encloses the base of the neck. The neck has four major compartments (Fig. 8.5), which are enclosed by an outer musculofascial collar: The vertebral compartment contains the cervical vertebrae and associated postural muscles. The visceral compartment contains important glands (thyroid, parathyroid, and thymus), and parts of the respiratory and digestive tracts that pass between the head and thorax. The two vascular compartments, one on each side, contain the major blood vessels and the vagus nerve.


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Anatomy_Gray. The two vascular compartments, one on each side, contain the major blood vessels and the vagus nerve. The neck contains two specialized structures associated with the digestive and respiratory tracts—the larynx and pharynx. The larynx (Fig. 8.6) is the upper part of the lower airway and is attached below to the top of the trachea and above, by a flexible membrane, to the hyoid bone, which in turn is attached to the floor of the oral cavity. A number of cartilages form a supportive framework for the larynx, which has a hollow central channel. The dimensions of this central channel can be adjusted by soft tissue structures associated with the laryngeal wall. The most important of these are two lateral vocal folds, which project toward each other from adjacent sides of the laryngeal cavity. The upper opening of the larynx (laryngeal inlet) is tilted posteriorly, and is continuous with the pharynx.


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Anatomy_Gray. The pharynx (Fig. 8.6) is a chamber in the shape of a half-cylinder with walls formed by muscles and fascia. Above, the walls are attached to the base of the skull, and below to the margins of the esophagus. On each side, the walls are attached to the lateral margins of the nasal cavities, the oral cavity, and the larynx. The two nasal cavities, the oral cavity, and the larynx therefore open into the anterior aspect of the pharynx, and the esophagus opens inferiorly. The part of the pharynx posterior to the nasal cavities is the nasopharynx. Those parts posterior to the oral cavity and larynx are the oropharynx and laryngopharynx, respectively. The head houses and protects the brain and all the receptor systems associated with the special senses—the nasal cavities associated with smell, the orbits with vision, the ears with hearing and balance, and the oral cavity with taste. Contains upper parts of respiratory


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Anatomy_Gray. Contains upper parts of respiratory The head contains the upper parts of the respiratory and digestive systems—the nasal and oral cavities—which have structural features for modifying the air or food passing into each system. The head and neck are involved in communication. Sounds produced by the larynx are modified in the pharynx and oral cavity to produce speech. In addition, the muscles of facial expression adjust the contours of the face to relay nonverbal signals. Positioning the head The neck supports and positions the head. Importantly, it enables an individual to position sensory systems in the head relative to environmental cues without moving the entire body. Connects the upper and lower respiratory and digestive tracts


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Anatomy_Gray. Connects the upper and lower respiratory and digestive tracts The neck contains specialized structures (pharynx and larynx) that connect the upper parts of the digestive and respiratory tracts (nasal and oral cavities) in the head, with the esophagus and trachea, which begin relatively low in the neck and pass into the thorax. The many bones of the head collectively form the skull (Fig. 8.7A). Most of these bones are interconnected by sutures, which are immovable fibrous joints (Fig. 8.7B). In the fetus and newborn, large membranous and unossified gaps (fontanelles) between the bones of the skull, particularly between the large flat bones that cover the top of the cranial cavity (Fig. 8.7C), allow: the head to deform during its passage through the birth canal, and postnatal growth.


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Anatomy_Gray. Most of the fontanelles close during the first year of life. Full ossification of the thin connective tissue ligaments separating the bones at the suture lines begins in the late twenties, and is normally completed in the fifth decade of life. There are only three pairs of synovial joints on each side in the head. The largest are the temporomandibular joints between the lower jaw (mandible) and the temporal bone. The other two synovial joints are between the three tiny bones in the middle ear, the malleus, incus, and stapes. The seven cervical vertebrae form the bony framework of the neck. Cervical vertebrae (Fig. 8.8A) are characterized by: small bodies, bifid spinous processes, and transverse processes that contain a foramen (foramen transversarium). Together the foramina transversaria form a longitudinal passage on each side of the cervical vertebral column for blood vessels (vertebral artery and veins) passing between the base of the neck and the cranial cavity.


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Anatomy_Gray. The typical transverse process of a cervical vertebra also has anterior and posterior tubercles for muscle attachment. The anterior tubercles are derived from the same embryological elements that give rise to ribs in the thoracic region. Occasionally, cervical ribs develop from these elements, particularly in association with the lower cervical vertebrae. The upper two cervical vertebrae (CI and CII) are modified for moving the head (Fig. 8.8B–E; see also Chapter 2). The hyoid bone is a small U-shaped bone (Fig. 8.9A) oriented in the horizontal plane just superior to the larynx, where it can be palpated and moved from side to side. The body of the hyoid bone is anterior and forms the base of the U. The two arms of the U (greater horns) project posteriorly from the lateral ends of the body. The hyoid bone does not articulate directly with any other skeletal elements in the head and neck.


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Anatomy_Gray. The two arms of the U (greater horns) project posteriorly from the lateral ends of the body. The hyoid bone does not articulate directly with any other skeletal elements in the head and neck. The hyoid bone is a highly movable and strong bony anchor for a number of muscles and soft tissue structures in the head and neck. Significantly, it is at the interface between three dynamic compartments: Superiorly, it is attached to the floor of the oral cavity. Inferiorly, it is attached to the larynx. Posteriorly, it is attached to the pharynx (Fig. 8.9B). The soft palate is a soft tissue flap-like structure “hinged” to the back of the hard palate (Fig. 8.10A) with a free posterior margin. It can be elevated and depressed by muscles (Fig. 8.10B). The soft palate and associated structures can be clearly seen through an open mouth. The skeletal muscles of the head and neck can be grouped on the basis of function, innervation, and embryological derivation. In the head


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Anatomy_Gray. The skeletal muscles of the head and neck can be grouped on the basis of function, innervation, and embryological derivation. In the head The muscle groups in the head include: the extra-ocular muscles (move the eyeball and open the upper eyelid), muscles of the middle ear (adjust the movement of the middle ear bones), muscles of facial expression (move the face), muscles of mastication (move the jaw—temporo- mandibular joint), muscles of the soft palate (elevate and depress the palate), and muscles of the tongue (move and change the contour of the tongue). In the neck In the neck, major muscle groups include: muscles of the pharynx (constrict and elevate the pharynx), muscles of the larynx (adjust the dimensions of the air pathway), strap muscles (position the larynx and hyoid bone in the neck), muscles of the outer cervical collar (move the head and upper limb), and postural muscles in the muscular compartment of the neck (position the neck and head).


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Anatomy_Gray. The superior thoracic aperture (thoracic inlet) opens directly into the base of the neck (Fig. 8.11). Structures passing between the head and thorax pass up and down through the superior thoracic aperture and the visceral compartment of the neck. At the base of the neck, the trachea is immediately anterior to the esophagus, which is directly anterior to the vertebral column. There are major veins, arteries, and nerves anterior and lateral to the trachea. There is an axillary inlet (gateway to the upper limb) on each side of the superior thoracic aperture at the base of the neck (Fig. 8.11): Structures such as blood vessels pass over rib I when passing between the axillary inlet and thorax. Cervical components of the brachial plexus pass directly from the neck through the axillary inlets to enter the upper limb. In the neck, the two important vertebral levels (Fig.


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Anatomy_Gray. Cervical components of the brachial plexus pass directly from the neck through the axillary inlets to enter the upper limb. In the neck, the two important vertebral levels (Fig. 8.12) are: between CIII and CIV, at approximately the superior border of the thyroid cartilage of the larynx (which can be palpated) and where the major artery on each side of the neck (the common carotid artery) bifurcates into internal and external carotid arteries; and between CV and CVI, which marks the lower limit of the pharynx and larynx, and the superior limit of the trachea and esophagus—the indentation between the cricoid cartilage of the larynx and the first tracheal ring can be palpated. The internal carotid artery has no branches in the neck and ascends into the skull to supply much of the brain. It also supplies the eye and orbit. Other regions of the head and neck are supplied by branches of the external carotid artery. Airway in the neck


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Anatomy_Gray. Airway in the neck The larynx (Fig. 8.13) and the trachea are anterior to the digestive tract in the neck, and can be accessed directly when upper parts of the system are blocked. A cricothyrotomy makes use of the easiest route of access through the cricothyroid ligament (cricovocal membrane, cricothyroid membrane) between the cricoid and thyroid cartilages of the larynx. The ligament can be palpated in the midline, and usually there are only small blood vessels, connective tissue, and skin (though occasionally, a small lobe of the thyroid gland—pyramidal lobe) overlying it. At a lower level, the airway can be accessed surgically through the anterior wall of the trachea by tracheostomy. This route of entry is complicated because large veins and part of the thyroid gland overlie this region. There are twelve pairs of cranial nerves and their defining feature is that they exit the cranial cavity through foramina or fissures.


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Anatomy_Gray. There are twelve pairs of cranial nerves and their defining feature is that they exit the cranial cavity through foramina or fissures. All cranial nerves innervate structures in the head or neck. In addition, the vagus nerve [X] descends through the neck and into the thorax and abdomen where it innervates viscera. Parasympathetic fibers in the head are carried out of the brain as part of four cranial nerves—the oculomotor nerve [III], the facial nerve [VII], the glossopharyngeal nerve [IX], and the vagus nerve [X] (Fig. 8.14). Parasympathetic fibers in the oculomotor nerve [III], the facial nerve [VII], and the glossopharyngeal nerve [IX] destined for target tissues in the head leave these nerves, and are distributed with branches of the trigeminal nerve [V]. The vagus nerve [X] leaves the head and neck to deliver parasympathetic fibers to the thoracic and abdominal viscera. There are eight cervical nerves (C1 to C8):


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Anatomy_Gray. The vagus nerve [X] leaves the head and neck to deliver parasympathetic fibers to the thoracic and abdominal viscera. There are eight cervical nerves (C1 to C8): C1 to C7 emerge from the vertebral canal above their respective vertebrae. C8 emerges between vertebrae CVII and TI (Fig. 8.15A). The anterior rami of C1 to C4 form the cervical plexus. The major branches from this plexus supply the strap muscles, the diaphragm (phrenic nerve), skin on the anterior and lateral parts of the neck, skin on the upper anterior thoracic wall, and skin on the inferior parts of the head (Fig. 8.15B). The anterior rami of C5 to C8, together with a large component of the anterior ramus of T1, form the brachial plexus, which innervates the upper limb. Functional separation of the digestive


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Anatomy_Gray. The anterior rami of C5 to C8, together with a large component of the anterior ramus of T1, form the brachial plexus, which innervates the upper limb. Functional separation of the digestive The pharynx is a common chamber for the digestive and respiratory tracts. Consequently, breathing can take place through the mouth as well as through the nose, and material from the oral cavity can potentially enter either the esophagus or the larynx. Importantly: The lower airway can be accessed through the oral cavity by intubation. The digestive tract (esophagus) can be accessed through the nasal cavity by feeding tubes. Normally, the soft palate, epiglottis, and soft tissue structures within the larynx act as valves to prevent food and liquid from entering lower parts of the respiratory tract (Fig. 8.16A).


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Anatomy_Gray. Normally, the soft palate, epiglottis, and soft tissue structures within the larynx act as valves to prevent food and liquid from entering lower parts of the respiratory tract (Fig. 8.16A). During normal breathing, the airway is open and air passes freely through the nasal cavities (or oral cavity), pharynx, larynx, and trachea (Fig. 8.16A). The lumen of the esophagus is normally closed because, unlike the airway, it has no skeletal support structures to hold it open. When the oral cavity is full of liquid or food, the soft palate is swung down (depressed) to close the oropharyngeal isthmus, thereby allowing manipulation of food and fluid in the oral cavity while breathing (Fig. 8.16C). When swallowing, the soft palate and parts of the larynx act as valves to ensure proper movement of food from the oral cavity into the esophagus (Fig. 8.16D).


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Anatomy_Gray. When swallowing, the soft palate and parts of the larynx act as valves to ensure proper movement of food from the oral cavity into the esophagus (Fig. 8.16D). The soft palate elevates to open the oropharyngeal isthmus while at the same time sealing off the nasal part of the pharynx from the oral part. This prevents food and fluid from moving upward into the nasopharynx and nasal cavities. The epiglottis of the larynx closes the laryngeal inlet and much of the laryngeal cavity becomes occluded by opposition of the vocal folds and soft tissue folds superior to them. In addition, the larynx is pulled up and forward to facilitate the moving of food and fluid over and around the closed larynx and into the esophagus.


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Anatomy_Gray. In newborns, the larynx is high in the neck and the epiglottis is above the level of the soft palate (Fig. 8.16E). Babies can therefore suckle and breathe at the same time. Liquid flows around the larynx without any danger of entering the airway. During the second year of life, the larynx descends into the low cervical position characteristic of adults. Triangles of the neck The two muscles (trapezius and sternocleidomastoid) that form part of the outer cervical collar divide the neck into anterior and posterior triangles on each side (Fig. 8.17). The boundaries of each anterior triangle are: the median vertical line of the neck, the inferior margin of the mandible, and the anterior margin of the sternocleidomastoid muscle. The posterior triangle is bounded by: the middle one-third of the clavicle, the anterior margin of the trapezius, and the posterior margin of the sternocleidomastoid.


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Anatomy_Gray. The posterior triangle is bounded by: the middle one-third of the clavicle, the anterior margin of the trapezius, and the posterior margin of the sternocleidomastoid. Major structures that pass between the head and thorax can be accessed through the anterior triangle. The posterior triangle in part lies over the axillary inlet, and is associated with structures (nerves and vessels) that pass into and out of the upper limb. The skull has 22 bones, excluding the ossicles of the ear. Except for the mandible, which forms the lower jaw, the bones of the skull are attached to each other by sutures, are immobile, and form the cranium. The cranium can be subdivided into: an upper domed part (the calvaria), which covers the cranial cavity containing the brain, a base that consists of the floor of the cranial cavity, and a lower anterior part—the facial skeleton (viscerocranium).


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Anatomy_Gray. The bones forming the calvaria are mainly the paired temporal and parietal bones, and parts of the unpaired frontal, sphenoid, and occipital bones. The bones forming the base of the cranium are mainly parts of the sphenoid, temporal, and occipital bones. The bones forming the facial skeleton are the paired nasal bones, palatine bones, lacrimal bones, zygomatic bones, maxillae and inferior nasal conchae and the unpaired vomer. The mandible is not part of the cranium nor part of the facial skeleton. The anterior view of the skull includes the forehead superiorly, and, inferiorly, the orbits, the nasal region, the part of the face between the orbit and the upper jaw, the upper jaw, and the lower jaw (Fig. 8.18). The forehead consists of the frontal bone, which also forms the superior part of the rim of each orbit (Fig. 8.18).


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Anatomy_Gray. The forehead consists of the frontal bone, which also forms the superior part of the rim of each orbit (Fig. 8.18). Just superior to the rim of the orbit on each side are the raised superciliary arches. These are more pronounced in men than in women. Between these arches is a small depression (the glabella). Clearly visible in the medial part of the superior rim of each orbit is the supra-orbital foramen (supra-orbital notch; Table 8.1). Medially, the frontal bone projects inferiorly forming a part of the medial rim of the orbit. Laterally, the zygomatic process of the frontal bone projects inferiorly forming the upper lateral rim of the orbit. This process articulates with the frontal process of the zygomatic bone. The lower lateral rim of the orbit, as well as the lateral part of the inferior rim of the orbit is formed by the zygomatic bone (the cheekbone).


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Anatomy_Gray. The lower lateral rim of the orbit, as well as the lateral part of the inferior rim of the orbit is formed by the zygomatic bone (the cheekbone). Superiorly, in the nasal region the paired nasal bones articulate with each other in the midline, and with the frontal bone superiorly. The center of the frontonasal suture formed by the articulation of the nasal bones and the frontal bone is the nasion. Laterally, each nasal bone articulates with the frontal process of each maxilla. Inferiorly, the piriform aperture is the large opening in the nasal region and the anterior opening of the nasal cavity. It is bounded superiorly by the nasal bones and laterally and inferiorly by each maxilla. Visible through the piriform aperture are the fused nasal crests, forming the lower part of the bony nasal septum and ending anteriorly as the anterior nasal spine, and the paired inferior nasal conchae.


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Anatomy_Gray. The part of the face between the orbit and the upper teeth and each upper jaw is formed by the paired maxillae. Superiorly, each maxilla contributes to the inferior and medial rims of the orbit. Laterally, the zygomatic process of each maxilla articulates with the zygomatic bone and medially, the frontal process of each maxilla articulates with the frontal bone. Inferiorly, the part of each maxilla, lateral to the opening of the nasal cavity, is the body of the maxilla. On the anterior surface of the body of the maxilla, just below the inferior rim of the orbit, is the infra-orbital foramen (Table 8.1). Inferiorly, each maxilla ends as the alveolar process, which contains the teeth and forms the upper jaw.


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Anatomy_Gray. Inferiorly, each maxilla ends as the alveolar process, which contains the teeth and forms the upper jaw. The lower jaw (mandible) is the most inferior structure in the anterior view of the skull. It consists of the body of the mandible anteriorly and the ramus of the mandible posteriorly. These meet posteriorly at the angle of the mandible. All these parts of the mandible are visible, to some extent, in the anterior view. The body of the mandible is arbitrarily divided into two parts: The lower part is the base of the mandible. The upper part is the alveolar part of the mandible. The alveolar part of the mandible contains the teeth and is resorbed when the teeth are removed. The base of the mandible has a midline swelling (the mental protuberance) on its anterior surface where the two sides of the mandible come together. Just lateral to the mental protuberance, on either side, are slightly more pronounced bumps (mental tubercles).


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Anatomy_Gray. Laterally, a mental foramen (Table 8.1) is visible halfway between the upper border of the alveolar part of the mandible and the lower border of the base of the mandible. Continuing past this foramen is a ridge (the oblique line) passing from the front of the ramus onto the body of the mandible. The oblique line is a point of attachment for muscles that depress the lower lip. The lateral view of the skull consists of the lateral wall of the cranium, which includes lateral portions of the calvaria and the facial skeleton, and half of the lower jaw (Fig. 8.19): Bones forming the lateral portion of the calvaria include the frontal, parietal, occipital, sphenoid, and temporal bones. Bones forming the visible part of the facial skeleton include the nasal, maxilla, and zygomatic bones. The mandible forms the visible part of the lower jaw. Lateral portion of the calvaria


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Anatomy_Gray. Bones forming the visible part of the facial skeleton include the nasal, maxilla, and zygomatic bones. The mandible forms the visible part of the lower jaw. Lateral portion of the calvaria The lateral portion of the calvaria begins anteriorly with the frontal bone. In upper regions, the frontal bone articulates with the parietal bone at the coronal suture. The parietal bone then articulates with the occipital bone at the lambdoid suture. In lower parts of the lateral portion of the calvaria, the frontal bone articulates with the greater wing of the sphenoid bone (Fig. 8.19), which then articulates with the parietal bone at the sphenoparietal suture, and with the anterior edge of the temporal bone at the sphenosquamous suture.


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Anatomy_Gray. The junction where the frontal, parietal, sphenoid, and temporal bones are in close proximity is the pterion. The clinical consequences of a skull fracture in this area can be very serious. The bone in this area is particularly thin and overlies the anterior division of the middle meningeal artery, which can be torn by a skull fracture in this area, resulting in an extradural hematoma. The final articulation across the lower part of the lateral portion of the calvaria is between the temporal bone and the occipital bone at the occipitomastoid suture. A major contributor to the lower portion of the lateral wall of the cranium is the temporal bone (Fig. 8.19), which consists of several parts:


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Anatomy_Gray. A major contributor to the lower portion of the lateral wall of the cranium is the temporal bone (Fig. 8.19), which consists of several parts: The squamous part has the appearance of a large flat plate, forms the anterior and superior parts of the temporal bone, contributes to the lateral wall of the cranium, and articulates anteriorly with the greater wing of the sphenoid bone at the sphenosquamous suture, and with the parietal bone superiorly at the squamous suture. The zygomatic process is an anterior bony projection from the lower surface of the squamous part of the temporal bone that initially projects laterally and then curves anteriorly to articulate with the temporal process of the zygomatic bone to form the zygomatic arch.


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Anatomy_Gray. Immediately below the origin of the zygomatic process from the squamous part of the temporal bone is the tympanic part of the temporal bone, and clearly visible on the surface of this part is the external acoustic opening leading to the external acoustic meatus (ear canal). The petromastoid part, which is usually separated into a petrous part and a mastoid part for descriptive purposes. The mastoid part is the most posterior part of the temporal bone, and is the only part of the petromastoid part of the temporal bone seen on a lateral view of the skull. It is continuous with the squamous part of the temporal bone anteriorly, and articulates with the parietal bone superiorly at the parietomastoid suture, and with the occipital bone posteriorly at the occipitomastoid suture. These two sutures are continuous with each other, and the parietomastoid suture is continuous with the squamous suture.


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Anatomy_Gray. Inferiorly, a large bony prominence (the mastoid process) projects from the inferior border of the mastoid part of the temporal bone. This is a point of attachment for several muscles. Medial to the mastoid process, the styloid process projects from the lower border of the temporal bone. Visible part of the facial skeleton The bones of the viscerocranium visible in a lateral view of the skull include the nasal, maxilla, and zygomatic bones (Fig. 8.19) as follows: A nasal bone anteriorly. The maxilla with its alveolar process containing teeth forming the upper jaw; anteriorly, it articulates with the nasal bone; superiorly, it contributes to the formation of the inferior and medial borders of the orbit; medially, its frontal process articulates with the frontal bone; laterally, its zygomatic process articulates with the zygomatic bone.


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Anatomy_Gray. The zygomatic bone, an irregularly shaped bone with a rounded lateral surface that forms the prominence of the cheek, is a visual centerpiece in this view— medially, it assists in the formation of the inferior rim of the orbit through its articulation with the zygomatic process of the maxilla; superiorly, its frontal process articulates with the zygomatic process of the frontal bone assisting in the formation of the lateral rim of the orbit; laterally, seen prominently in this view of the skull, the horizontal temporal process of the zygomatic bone projects backward to articulate with the zygomatic process of the temporal bone and so form the zygomatic arch. Usually a small foramen (the zygomaticofacial foramen; Table 8.1) is visible on the lateral surface of the zygomatic bone. A zygomaticotemporal foramen is present on the medial deep surface of the bone.


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Anatomy_Gray. The final bony structure visible in a lateral view of the skull is the mandible. Inferiorly in the anterior part of this view, it consists of the anterior body of the mandible, a posterior ramus of the mandible, and the angle of the mandible where the inferior margin of the mandible meets the posterior margin of the ramus (Fig. 8.19). The teeth are in the alveolar part of the body of the mandible and the mental protuberance is visible in this view. The mental foramen is on the lateral surface of the body, and on the superior part of the ramus condylar and coronoid processes extend upward. The condylar process is involved in articulation of the mandible with the temporal bone, and the coronoid process is the point of attachment for the temporalis muscle. The occipital, parietal, and temporal bones are seen in the posterior view of the skull.


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Anatomy_Gray. The occipital, parietal, and temporal bones are seen in the posterior view of the skull. Centrally the flat or squamous part of the occipital bone is the main structure in this view of the skull (Fig. 8.20). It articulates superiorly with the paired parietal bones at the lambdoid suture and laterally with each temporal bone at the occipitomastoid sutures. Along the lambdoid suture small islands of bone (sutural bones or wormian bones) may be observed. Several bony landmarks are visible on the occipital bone. There is a midline projection (the external occipital protuberance) with curved lines extending laterally from it (superior nuchal lines). The most prominent point of the external occipital protuberance is the inion. About 1 inch (2.5 cm) below the superior nuchal lines two additional lines (the inferior nuchal lines) curve laterally. Extending downward from the external occipital protuberance is the external occipital crest.


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Anatomy_Gray. Laterally, the temporal bones are visible in the posterior view of the skull, with the mastoid processes being the prominent feature (Fig. 8.20). On the inferomedial border of each mastoid process is a notch (the mastoid notch), which is a point of attachment for the posterior belly of the digastric muscle. The frontal bone, parietal bones, and occipital bone are seen in a superior view of the skull (Fig. 8.21). These bones make up the superior part of the calvaria or the calva (skullcap). In an anterior to posterior direction: The unpaired frontal bone articulates with the paired parietal bones at the coronal suture. The two parietal bones articulate with each other in the midline at the sagittal suture. The parietal bones articulate with the unpaired occipital bone at the lambdoid suture. The junction of the sagittal and coronal sutures is the bregma, and the junction of the sagittal and lambdoid sutures is the lambda.


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Anatomy_Gray. The junction of the sagittal and coronal sutures is the bregma, and the junction of the sagittal and lambdoid sutures is the lambda. The only foramina visible in this view of the skull may be the paired parietal foramina, posteriorly, one on each parietal bone just lateral to the sagittal suture (Fig. 8.21). The bones making up the calvaria (Fig. 8.22) are unique in their structure, consisting of dense internal and external tables of compact bone separated by a layer of spongy bone (the diploë). The base of the skull is seen in the inferior view and extends anteriorly from the middle incisor teeth posteriorly to the superior nuchal lines and laterally to the mastoid processes and zygomatic arches (Fig. 8.23).


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Anatomy_Gray. For descriptive purposes the base of the skull is often divided into: an anterior part, which includes the teeth and the hard palate, a middle part, which extends from behind the hard palate to the anterior margin of the foramen magnum, and a posterior part, which extends from the anterior edge of the foramen magnum to the superior nuchal lines. The main features of the anterior part of the base of the skull are the teeth and the hard palate. The teeth project from the alveolar processes of the two maxillae. These processes are together arranged in a U-shaped alveolar arch that borders the hard palate on three sides (Fig. 8.23). The hard palate is composed of the palatine processes of each maxilla anteriorly and the horizontal plates of each palatine bone posteriorly.


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Anatomy_Gray. The hard palate is composed of the palatine processes of each maxilla anteriorly and the horizontal plates of each palatine bone posteriorly. The paired palatine processes of each maxilla meet in the midline at the intermaxillary suture, the paired maxillae and the paired palatine bones meet at the palatomaxillary suture, and the paired horizontal plates of each palatine bone meet in the midline at the interpalatine suture.


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Anatomy_Gray. Several additional features are also visible when the hard palate is examined: the incisive fossa in the anterior midline immediately posterior to the teeth, the walls of which contain incisive foramina (the openings of the incisive canals, which are passageways between the hard palate and nasal cavity); the greater palatine foramina near the posterolateral border of the hard palate on each side, which lead to greater palatine canals; just posterior to the greater palatine foramina, the lesser palatine foramina in the pyramidal process of each palatine bone, which lead to lesser palatine canals; a midline pointed projection (the posterior nasal spine) in the free posterior border of the hard palate. The middle part of the base of the skull is complex: Forming the anterior half are the vomer and sphenoid bones. Forming the posterior half are the occipital and paired temporal bones.


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Anatomy_Gray. The middle part of the base of the skull is complex: Forming the anterior half are the vomer and sphenoid bones. Forming the posterior half are the occipital and paired temporal bones. Anteriorly, the small vomer is in the midline, resting on the sphenoid bone (Fig. 8.23). It contributes to the formation of the bony nasal septum separating the two choanae. Most of the anterior part of the middle part of the base of the skull consists of the sphenoid bone. The sphenoid bone is made up of a centrally placed body, paired greater and lesser wings projecting laterally from the body, and two downward projecting pterygoid processes immediately lateral to each choana. Three parts of the sphenoid bone, the body, greater wings, and pterygoid processes, are seen in the inferior view of the skull (Fig. 8.23). The lesser wing of the sphenoid is not seen in the inferior view. The body of the sphenoid is a centrally placed cube of bone containing two large air sinuses separated by a septum.


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Anatomy_Gray. The body of the sphenoid is a centrally placed cube of bone containing two large air sinuses separated by a septum. It articulates anteriorly with the vomer, ethmoid, and palatine bones, posterolaterally with the temporal bones, and posteriorly with the occipital bone. Extending downward from the junction of the body and the greater wings are the pterygoid processes (Fig. 8.23). Each of these processes consists of a narrow medial plate and broader lateral plate separated by the pterygoid fossa. Each medial plate of the pterygoid process ends inferiorly with a hook-like projection, the pterygoid hamulus, and divides superiorly to form the small, shallow scaphoid fossa. Just superior to the scaphoid fossa, at the root of the medial plate of the pterygoid process is the opening of the pterygoid canal, which passes forward from near the anterior margin of the foramen lacerum.


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Anatomy_Gray. Lateral to the lateral plate of the pterygoid process is the greater wing of the sphenoid (Fig. 8.23), which not only forms a part of the base of the skull but also continues laterally to form part of the lateral wall of the skull. It articulates laterally and posteriorly with parts of the temporal bone. Important features visible on the surface of the greater wing in an inferior view of the skull are the foramen ovale and the foramen spinosum on the posterolateral border extending outward from the upper end of the lateral plate of the pterygoid process. In the posterior half of the middle part of the base of the skull are the occipital bone and the paired temporal bones (Fig. 8.23). The occipital bone, or more specifically its basilar part, is in the midline immediately posterior to the body of the sphenoid. It extends posteriorly to the foramen magnum and is bounded laterally by the temporal bones.


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Anatomy_Gray. Prominent on the basilar part of the occipital bone is the pharyngeal tubercle, a bony protuberance for the attachment of parts of the pharynx to the base of the skull (Fig. 8.23). Immediately lateral to the basilar part of the occipital bone is the petrous part of the petromastoid part of each temporal bone. Wedge-shaped in its appearance, with its apex anteromedial, the petrous part of the temporal bone is between the greater wing of the sphenoid anteriorly and the basilar part of the occipital bone posteriorly. The apex forms one of the boundaries of the foramen lacerum, an irregular opening filled in life with cartilage (Fig. 8.23). The other boundaries of the foramen lacerum are the basilar part of the occipital bone medially and the body of the sphenoid anteriorly. Posterolateral from the foramen lacerum along the petrous part of the temporal bone is the large circular opening for the carotid canal.


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Anatomy_Gray. Posterolateral from the foramen lacerum along the petrous part of the temporal bone is the large circular opening for the carotid canal. Between the petrous part of the temporal bone and the greater wing of the sphenoid is a groove for the cartilaginous part of the pharyngotympanic tube (auditory tube). This groove continues posterolaterally into a bony canal in the petrous part of the temporal bone for the pharyngotympanic tube. Just lateral to the greater wing of the sphenoid is the squamous part of the temporal bone, which participates in the temporomandibular joint. It contains the mandibular fossa, which is a concavity where the head of the mandible articulates with the base of the skull. An important feature of this articulation is the prominent articular tubercle, which is the downward projection of the anterior border of the mandibular fossa (Fig. 8.23).


Anatomy_Gray

Anatomy_Gray. The posterior part of the base of the skull extends from the anterior edge of the foramen magnum posteriorly to the superior nuchal lines (Fig. 8.23). It consists of parts of the occipital bone centrally and the temporal bones laterally. The occipital bone is the major bony element of this part of the base of the skull (Fig. 8.23). It has four parts organized around the foramen magnum, which is a prominent feature of this part of the base of the skull and through which the brain and spinal cord are continuous. The parts of the occipital bone are the squamous part, which is posterior to the foramen magnum, the lateral parts, which are lateral to the foramen magnum, and the basilar part, which is anterior to the foramen magnum (Fig. 8.23). The squamous and lateral parts are components of the posterior part of the base of the skull.


Anatomy_Gray

Anatomy_Gray. The squamous and lateral parts are components of the posterior part of the base of the skull. The most visible feature of the squamous part of the occipital bone when examining the inferior view of the skull is a ridge of bone (the external occipital crest), which extends downward from the external occipital protuberance toward the foramen magnum. The inferior nuchal lines arc laterally from the midpoint of the crest. Immediately lateral to the foramen magnum are the lateral parts of the occipital bones, which contain numerous important structural features.


Anatomy_Gray

Anatomy_Gray. Immediately lateral to the foramen magnum are the lateral parts of the occipital bones, which contain numerous important structural features. On each anterolateral border of the foramen magnum are the rounded occipital condyles (Fig. 8.23). These paired structures articulate with the atlas (vertebra CI). Posterior to each condyle is a depression (the condylar fossa) containing a condylar canal, and anterior and superior to each condyle is the large hypoglossal canal. Lateral to each hypoglossal canal is a large, irregular jugular foramen formed by opposition of the jugular notch of the occipital bone and jugular notch of the temporal bone. Laterally in the posterior part of the base of the skull is the temporal bone. The parts of the temporal bone seen in this location are the mastoid part of the petromastoid part and the styloid process (Fig. 8.23).


Anatomy_Gray

Anatomy_Gray. The lateral edge of the mastoid part is identified by the large cone-shaped mastoid process projecting from its inferior surface. This prominent bony structure is the point of attachment for several muscles. On the medial aspect of the mastoid process is the deep mastoid notch, which is also an attachment point for a muscle. Anteromedial to the mastoid process is the needle-shaped styloid process projecting from the lower border of the temporal bone. The styloid process is also a point of attachment for numerous muscles and ligaments. Finally, between the styloid process and the mastoid process is the stylomastoid foramen. The cranial cavity is the space within the cranium that contains the brain, meninges, proximal parts of the cranial nerves, blood vessels, and cranial venous sinuses.


Anatomy_Gray

Anatomy_Gray. The cranial cavity is the space within the cranium that contains the brain, meninges, proximal parts of the cranial nerves, blood vessels, and cranial venous sinuses. The calvaria is the dome-shaped roof that protects the superior aspect of the brain. It consists mainly of the frontal bone anteriorly, the paired parietal bones in the middle, and the occipital bone posteriorly (Fig. 8.24). Sutures visible internally include: the coronal suture, between the frontal and parietal bones, the sagittal suture, between the paired parietal bones, and the lambdoid suture, between the parietal and occipital bones. Visible junctions of these sutures are the bregma, where the coronal and sagittal sutures meet, and the lambda, where the lambdoid and sagittal sutures meet. Other markings on the internal surface of the calva include bony ridges and numerous grooves and pits.


Anatomy_Gray

Anatomy_Gray. From anterior to posterior, features seen on the bony roof of the cranial cavity are: a midline ridge of bone extending from the surface of the frontal bone (the frontal crest), which is a point of attachment for the falx cerebri (a specialization of the dura mater that partially separates the two cerebral hemispheres); at the superior point of the termination of the frontal crest the beginning of the groove for the superior sagittal sinus, which widens and deepens posteriorly and marks the position of the superior sagittal sinus (an intradural venous structure); on either side of the groove for the superior sagittal sinus throughout its course, a small number of depressions and pits (the granular foveolae), which mark the location of arachnoid granulations (prominent structures readily identifiable when a brain with its meningeal coverings is examined; the arachnoid granulations are involved in the reabsorption of cerebrospinal fluid); and on the lateral aspects of the roof of the


Anatomy_Gray

Anatomy_Gray. identifiable when a brain with its meningeal coverings is examined; the arachnoid granulations are involved in the reabsorption of cerebrospinal fluid); and on the lateral aspects of the roof of the cranial cavity, smaller grooves created by various meningeal vessels.


Anatomy_Gray

Anatomy_Gray. The floor of the cranial cavity is divided into anterior, middle, and posterior cranial fossae. Parts of the frontal, ethmoid, and sphenoid bones form the anterior cranial fossa (Fig. 8.25). Its floor is composed of: frontal bone in the anterior and lateral direction, ethmoid bone in the midline, and two parts of the sphenoid bone posteriorly, the body (midline) and the lesser wings (laterally). The anterior cranial fossa is above the nasal cavity and the orbits, and it is filled by the frontal lobes of the cerebral hemispheres. Anteriorly, a small wedge-shaped midline crest of bone (the frontal crest) projects from the frontal bone. This is a point of attachment for the falx cerebri. Immediately posterior to the frontal crest is the foramen cecum (Table 8.2). This foramen between the frontal and ethmoid bones may transmit emissary veins connecting the nasal cavity with the superior sagittal sinus.


Anatomy_Gray

Anatomy_Gray. Posterior to the frontal crest is a prominent wedge of bone projecting superiorly from the ethmoid (the crista galli). This is another point of attachment for the falx cerebri, which is the vertical extension of dura mater partially separating the two cerebral hemispheres. Lateral to the crista galli is the cribriform plate of the ethmoid bone (Fig. 8.25). This is a sieve-like structure, which allows small olfactory nerve fibers to pass through its foramina from the nasal mucosa to the olfactory bulb. The olfactory nerves are commonly referred to collectively as the olfactory nerve [I].


Anatomy_Gray

Anatomy_Gray. On each side of the ethmoid, the floor of the anterior cranial fossa is formed by relatively thin plates of frontal bone (the orbital part of the frontal bone), which also forms the roof of the orbit below. Posterior to both the frontal and ethmoid bones, the rest of the floor of the anterior cranial fossa is formed by the body and lesser wings of the sphenoid. In the midline, the body extends anteriorly between the orbital parts of the frontal bone to reach the ethmoid bone and posteriorly it extends into the middle cranial fossa. The boundary between the anterior and middle cranial fossae in the midline is the anterior edge of the prechiasmatic sulcus, a smooth groove stretching between the optic canals across the body of the sphenoid. Lesser wings of the sphenoid The two lesser wings of the sphenoid project laterally from the body of the sphenoid and form a distinct boundary between the lateral parts of the anterior and middle cranial fossae.


Anatomy_Gray

Anatomy_Gray. The two lesser wings of the sphenoid project laterally from the body of the sphenoid and form a distinct boundary between the lateral parts of the anterior and middle cranial fossae. Overhanging the anterior part of the middle cranial fossae, each lesser wing ends laterally as a sharp point at the junction of the frontal bone and the greater wing of the sphenoid near the upper lateral edge of the superior orbital fissure that is formed between the greater and lesser wings.


Anatomy_Gray

Anatomy_Gray. Medially each lesser wing widens, curves posteriorly, and ends as a rounded anterior clinoid process (Fig. 8.25). These processes serve as the anterior point of attachment for the tentorium cerebelli, which is a sheet of dura that separates the posterior part of the cerebral hemispheres from the cerebellum. Just anterior to each anterior clinoid process is a circular opening in the lesser wing of the sphenoid (the optic canal), through which the ophthalmic artery and optic nerve [II] pass as they exit the cranial cavity to enter the orbit. The optic canals are usually included in the middle cranial fossa. The middle cranial fossa consists of parts of the sphenoid and temporal bones (Fig. 8.26). The boundary between the anterior and middle cranial fossae in the midline is the anterior edge of the prechiasmatic sulcus, which is a smooth groove stretching between the optic canals across the body of the sphenoid.


Anatomy_Gray

Anatomy_Gray. The posterior boundaries of the middle cranial fossa are formed by the anterior surface, as high as the superior border, of the petrous part of the petromastoid part of the temporal bone. The floor in the midline of the middle cranial fossa is elevated and formed by the body of the sphenoid. Lateral to this are large depressions formed on either side by the greater wing of the sphenoid and the squamous part of the temporal bone. These depressions contain the temporal lobes of the brain. Just posterior to the chiasmatic sulcus is the uniquely modified remainder of the body of the sphenoid (the sella turcica), which consists of a deep central area (the hypophyseal fossa) containing the pituitary gland with anterior and posterior vertical walls of bone (Fig. 8.26). The anterior wall of the sella is vertical in position with its superior extent visible as a slight elevation (the tuberculum sellae) at the posterior edge of the chiasmatic sulcus.


Anatomy_Gray

Anatomy_Gray. The anterior wall of the sella is vertical in position with its superior extent visible as a slight elevation (the tuberculum sellae) at the posterior edge of the chiasmatic sulcus. Lateral projections from the corners of the tuberculum sellae (the middle clinoid processes) are sometimes evident. The posterior wall of the sella turcica is the dorsum sellae, a large ridge of bone projecting upward and forward. At the top of this bony ridge the lateral edges contain rounded projections (the posterior clinoid processes), which are points of attachment, like the anterior clinoid processes, for the tentorium cerebelli. Lateral to each side of the body of the sphenoid, the floor of the middle cranial fossa is formed on either side by the greater wing of the sphenoid (Fig. 8.26).


Anatomy_Gray

Anatomy_Gray. Lateral to each side of the body of the sphenoid, the floor of the middle cranial fossa is formed on either side by the greater wing of the sphenoid (Fig. 8.26). A diagonal gap, the superior orbital fissure, separates the greater wing of the sphenoid from the lesser wing and is a major passageway between the middle cranial fossa and the orbit. Passing through the fissure are the oculomotor nerve [III], the trochlear nerve [IV], the ophthalmic nerve [V1], the abducent nerve [VI], and ophthalmic veins. Posterior to the medial end of the superior orbital fissure on the floor of the middle cranial fossa is a rounded foramen projecting in an anterior direction (the foramen rotundum), through which the maxillary nerve [V2] passes from the middle cranial fossa to the pterygopalatine fossa.


Anatomy_Gray

Anatomy_Gray. Posterolateral to the foramen rotundum is a large oval opening (the foramen ovale), which allows structures to pass between the extracranial infratemporal fossa and the middle cranial fossa. The mandibular nerve [V3], lesser petrosal nerve (carrying fibers from the tympanic plexus that originally came from the glossopharyngeal nerve [IX]) and, occasionally, a small vessel (the accessory middle meningeal artery), pass through this foramen. Posterolateral from the foramen ovale is the small foramen spinosum (Fig. 8.26). This opening also connects the infratemporal fossa with the middle cranial fossa. The middle meningeal artery and its associated veins pass through this foramen and, once inside, the groove for the middle meningeal artery across the floor and lateral wall of the middle cranial fossa clearly marks their path.


Anatomy_Gray

Anatomy_Gray. Posteromedial to the foramen ovale is the rounded intracranial opening of the carotid canal. Directly inferior to this opening is an irregular foramen (the foramen lacerum) (Fig. 8.26). Clearly observed in the inferior view of the skull, the foramen lacerum is closed in life by a cartilaginous plug, and no structures pass through it completely. The posterior boundary of the middle cranial fossa is formed by the anterior surface of the petrous part of the petromastoid part of the temporal bone. Medially, there is a slight depression (trigeminal impression) in the anterior surface of the petrous part of the temporal bone (Fig. 8.26), which marks the location of the sensory ganglion for the trigeminal nerve [V].


Anatomy_Gray

Anatomy_Gray. Lateral to the trigeminal impression and on the anterior surface of the petrous part of the temporal bone is a small linear groove that passes in a superolateral direction and ends in a foramen (the groove and hiatus for the greater petrosal nerve). The greater petrosal nerve is a branch of the facial nerve [VII]. Anterolateral to the groove for the greater petrosal nerve is a second, smaller groove and hiatus for the lesser petrosal nerve, a branch from the tympanic plexus carrying fibers that originally came from the glossopharyngeal nerve [IX] (Fig. 8.26). Above and lateral to the small openings for the greater and lesser petrosal nerves, near the superior ridge of the petrous part of the temporal bone, is a rounded protrusion of bone (the arcuate eminence) produced by the underlying anterior semicircular canal of the inner ear.


Anatomy_Gray

Anatomy_Gray. Just anterior and lateral to the arcuate eminence the anterior surface of the petrous part of the temporal bone is slightly depressed. This region is the tegmen tympani, and marks the thin bony roof of the middle ear cavity. The posterior cranial fossa consists mostly of parts of the temporal and occipital bones, with small contributions from the sphenoid and parietal bones (Fig. 8.27). It is the largest and deepest of the three cranial fossae and contains the brainstem (midbrain, pons, and medulla) and the cerebellum. The anterior boundaries of the posterior cranial fossa in the midline are the dorsum sellae and the clivus (Fig. 8.27). The clivus is a slope of bone that extends upward from the foramen magnum. It is formed by contributions from the body of the sphenoid and from the basilar part of the occipital bone. Laterally the anterior boundaries of the posterior cranial fossa are the superior border of the petrous part of the petromastoid part of the temporal bone.


Anatomy_Gray

Anatomy_Gray. Laterally the anterior boundaries of the posterior cranial fossa are the superior border of the petrous part of the petromastoid part of the temporal bone. Posteriorly the squamous part of the occipital bone to the level of the transverse groove is the major boundary, while laterally the petromastoid part of the temporal bone and small parts of the occipital and parietal bones border the fossa. Centrally, in the deepest part of the posterior cranial fossa, is the largest foramen in the skull, the foramen magnum. It is surrounded by the basilar part of the occipital bone anteriorly, the lateral parts of the occipital bone on either side, and the squamous part of the occipital bone posteriorly. The spinal cord passes superiorly through the foramen magnum to continue as the brainstem. Also passing through the foramen magnum are the vertebral arteries, the meninges, and the spinal roots of the accessory nerve [XI].


Anatomy_Gray

Anatomy_Gray. Also passing through the foramen magnum are the vertebral arteries, the meninges, and the spinal roots of the accessory nerve [XI]. The clivus slopes upward from the foramen magnum. Lateral to the clivus is a groove for the inferior petrosal sinus between the basilar part of the occipital bone and the petrous part of the petromastoid part of the temporal bone (Fig. 8.27). Laterally, across the upper half of the posterior surface of the petrous part of the temporal bone, is an oval foramen (the internal acoustic meatus). The facial [VII] and vestibulocochlear [VIII] nerves, and the labyrinthine artery pass through it. Inferior to the internal acoustic meatus the temporal bone is separated from the occipital bone by the large jugular foramen (Fig. 8.27). Leading to this foramen from the medial side is the groove for the inferior petrosal sinus, and from the lateral side the groove for the sigmoid sinus.


Anatomy_Gray

Anatomy_Gray. The sigmoid sinus passes into the jugular foramen, and is continuous with the internal jugular vein, while the inferior petrosal sinus empties into the internal jugular vein in the area of the jugular foramen. Also passing through the jugular foramen are the glossopharyngeal nerve [IX], the vagus nerve [X], and the accessory nerve [XI]. Medial to the jugular foramen is a large rounded mound of the occipital bone (the jugular tubercle). Just inferior to this, and superior to the foramen magnum, is the hypoglossal canal, through which the hypoglossal nerve [XII] leaves the posterior cranial fossa, and a meningeal branch of the ascending pharyngeal artery enters the posterior cranial fossa. Just posterolateral to the hypoglossal canal is the small condylar canal that, when present, transmits an emissary vein. Squamous part of the occipital bone The squamous part of the occipital bone has several prominent features (Fig. 8.27):


Anatomy_Gray

Anatomy_Gray. Squamous part of the occipital bone The squamous part of the occipital bone has several prominent features (Fig. 8.27): Running upward in the midline from the foramen magnum is the internal occipital crest. On either side of the internal occipital crest, the floor of the posterior cranial fossa is concave to accommodate the cerebellar hemispheres. The internal occipital crest ends superiorly in a bony prominence (the internal occipital protuberance). Extending laterally from the internal occipital protuberance are grooves produced by the transverse sinuses, which continue laterally, eventually joining a groove for each sigmoid sinus—each of these grooves then turns inferiorly toward the jugular foramina. The transverse and sigmoid sinuses are intradural venous sinuses. Foramina and fissures through which major structures enter and leave the cranial cavity


Anatomy_Gray

Anatomy_Gray. The transverse and sigmoid sinuses are intradural venous sinuses. Foramina and fissures through which major structures enter and leave the cranial cavity Foramina and fissures through which major structures pass between the cranial cavity and other regions are summarized in Fig. 8.28. The brain, as well as the spinal cord, is surrounded by three layers of membranes (the meninges, Fig. 8.31A)—a tough, outer layer (the dura mater), a delicate, middle layer (the arachnoid mater), and an inner layer firmly attached to the surface of the brain (the pia mater). The cranial meninges are continuous with, and similar to, the spinal meninges through the foramen magnum, with one important distinction—the cranial dura mater consists of two layers, and only one of these is continuous through the foramen magnum (Fig. 8.31B). The cranial dura mater is a thick, tough, outer covering of the brain. It consists of an outer periosteal layer and an inner meningeal layer (Fig. 8.31A):


Anatomy_Gray

Anatomy_Gray. The cranial dura mater is a thick, tough, outer covering of the brain. It consists of an outer periosteal layer and an inner meningeal layer (Fig. 8.31A): The outer periosteal layer is firmly attached to the skull, is the periosteum of the cranial cavity, contains the meningeal arteries, and is continuous with the periosteum on the outer surface of the skull at the foramen magnum and other intracranial foramina (Fig. 8.31B). The inner meningeal layer is in close contact with the arachnoid mater and is continuous with the spinal dura mater through the foramen magnum. The two layers of dura separate from each other at numerous locations to form two unique types of structures (Fig. 8.31A): dural partitions, which project inward and incompletely separate parts of the brain, and intracranial venous structures.


Anatomy_Gray

Anatomy_Gray. The dural partitions project into the cranial cavity and partially subdivide the cranial cavity. They include the falx cerebri, tentorium cerebelli, falx cerebelli, and diaphragma sellae. The falx cerebri (Fig. 8.32) is a crescent-shaped downward projection of meningeal dura mater from the dura lining the calva that passes between the two cerebral hemispheres. It is attached anteriorly to the crista galli of the ethmoid bone and frontal crest of the frontal bone. Posteriorly it is attached to and blends with the tentorium cerebelli.


Anatomy_Gray

Anatomy_Gray. The tentorium cerebelli (Fig. 8.32) is a horizontal projection of the meningeal dura mater that covers and separates the cerebellum in the posterior cranial fossa from the posterior parts of the cerebral hemispheres. It is attached posteriorly to the occipital bone along the grooves for the transverse sinuses. Laterally, it is attached to the superior border of the petrous part of the temporal bone, ending anteriorly at the anterior and posterior clinoid processes. The anterior and medial borders of the tentorium cerebelli are free, forming an oval opening in the midline (the tentorial notch), through which the midbrain passes. The falx cerebelli (Fig. 8.32) is a small midline projection of meningeal dura mater in the posterior cranial fossa. It is attached posteriorly to the internal occipital crest of the occipital bone and superiorly to the tentorium cerebelli. Its anterior edge is free and is between the two cerebellar hemispheres.


Anatomy_Gray

Anatomy_Gray. The final dural projection is the diaphragma sellae (Fig. 8.32). This small horizontal shelf of meningeal dura mater covers the hypophyseal fossa in the sella turcica of the sphenoid bone. There is an opening in the center of the diaphragma sellae through which passes the infundibulum, connecting the pituitary gland with the base of the brain, and any accompanying blood vessels. The arterial supply to the dura mater (Fig. 8.33) travels in the outer periosteal layer of the dura and consists of: anterior meningeal arteries in the anterior cranial fossa, the middle and accessory meningeal arteries in the middle cranial fossa, and the posterior meningeal artery and other meningeal branches in the posterior cranial fossa. All are small arteries except for the middle meningeal artery, which is much larger and supplies the greatest part of the dura. The anterior meningeal arteries are branches of the ethmoidal arteries.


Anatomy_Gray

Anatomy_Gray. The anterior meningeal arteries are branches of the ethmoidal arteries. The middle meningeal artery is a branch of the maxillary artery. It enters the middle cranial fossa through the foramen spinosum and divides into anterior and posterior branches: The anterior branch passes in an almost vertical direction to reach the vertex of the skull, crossing the pterion during its course. The posterior branch passes in a posterosuperior direction, supplying this region of the middle cranial fossa. The accessory meningeal artery is usually a small branch of the maxillary artery that enters the middle cranial fossa through the foramen ovale and supplies areas medial to this foramen. The posterior meningeal artery and other meningeal branches supplying the dura mater in the posterior cranial fossa come from several sources (Fig. 8.33): The posterior meningeal artery, the terminal branch of the ascending pharyngeal artery, enters the posterior cranial fossa through the jugular foramen.


Anatomy_Gray

Anatomy_Gray. The posterior meningeal artery, the terminal branch of the ascending pharyngeal artery, enters the posterior cranial fossa through the jugular foramen. A meningeal branch from the ascending pharyngeal artery enters the posterior cranial fossa through the hypoglossal canal. Meningeal branches from the occipital artery enter the posterior cranial fossa through the jugular foramen and the mastoid foramen. A meningeal branch from the vertebral artery arises as the vertebral artery enters the posterior cranial fossa through the foramen magnum. Innervation of the dura mater (Fig. 8.34) is by small meningeal branches of all three divisions of the trigeminal nerve [V1, V2, and V3], the vagus nerve [X], and the first, second, and, sometimes, third cervical nerves. (Possible involvement of the glossopharyngeal [IX] and hypoglossal nerves [XII] in the posterior cranial fossa has also been reported.)


Anatomy_Gray

Anatomy_Gray. In the anterior cranial fossa meningeal branches from the ethmoidal nerves, which are branches of the ophthalmic nerve [V1], supply the floor and the anterior part of the falx cerebri. Additionally, a meningeal branch of the ophthalmic nerve [V1] turns and runs posteriorly, supplying the tentorium cerebelli and the posterior part of the falx cerebri. The middle cranial fossa is supplied medially by meningeal branches from the maxillary nerve [V2] and laterally, along the distribution of the middle meningeal artery, by meningeal branches from the mandibular nerve [V3]. The posterior cranial fossa is supplied by meningeal branches from the first, second, and, sometimes, third cervical nerves, which enter the fossa through the foramen magnum, the hypoglossal canal, and the jugular foramen. Meningeal branches of the vagus nerve [X] have also been described. (Possible contributions from the glossopharyngeal [IX] and hypoglossal [XII] nerves have also been reported.)


Anatomy_Gray

Anatomy_Gray. The arachnoid mater is a thin, avascular membrane that lines, but is not adherent to, the inner surface of the dura mater (Fig. 8.35). From its inner surface thin processes or trabeculae extend downward, cross the subarachnoid space, and become continuous with the pia mater. Unlike the pia, the arachnoid does not enter the grooves or fissures of the brain, except for the longitudinal fissure between the two cerebral hemispheres. The pia mater is a thin, delicate membrane that closely invests the surface of the brain (Fig. 8.35). It follows the contours of the brain, entering the grooves and fissures on its surface, and is closely applied to the roots of the cranial nerves at their origins. Arrangement of meninges and spaces There is a unique arrangement of meninges coupled with real and potential spaces within the cranial cavity (Fig. 8.35). A potential space is related to the dura mater, while a real space exists between the arachnoid mater and the pia mater.


Anatomy_Gray

Anatomy_Gray. A potential space is related to the dura mater, while a real space exists between the arachnoid mater and the pia mater. The potential space between dura mater and bone is the extradural space (Fig. 8.35). Normally, the outer or periosteal layer of dura mater is firmly attached to the bones surrounding the cranial cavity. This potential space between dura and bone can become a fluid-filled actual space when a traumatic event results in a vascular hemorrhage. Bleeding into the extradural space primarily due to rupture of a meningeal artery or less often from a torn dural venous sinus results in an extradural hematoma.


Anatomy_Gray

Anatomy_Gray. Anatomically, a true subdural space does not exist. Blood collecting in this region (subdural hematoma) due to injury represents a dissection of the dural border cell layer, which is the innermost lining of the meningeal dura. Dural border cells are flattened cells surrounded by extracellular spaces filled with amorphous material. While very infrequent, an occasional cell junction may be seen between these cells and the underlying arachnoid layer. Bleeding due to the tearing of a cerebral vein as it crosses through the dura to enter a dural venous sinus can result in a subdural hematoma.