Section 1 of Grey's Anatomy, Part 2. This is a LibriVox recording. All LibriVox recordings are in the public domain. For more information or to volunteer, please visit LibriVox.org. Recorded by Laurie Ann Walden. Anatomy of the Human Body, Part 2 by Henry Gray. Sin Dismology, Introduction. The bones of the skeleton are joined to one another at different parts of their surfaces, and such connections are termed joints or articulations. Where the joints are immovable, as in the articulations between practically all the bones of the skull, the adjacent margins of the bones are almost in contact, being separated merely by a thin layer of fibrous membrane named the sutral ligament. In certain regions at the base of the skull, this fibrous membrane is replaced by a layer of cartilage, where slight movement combined with great strength is required, the osseous surfaces are united by tough and elastic fibrocartilages, as in the joints between the vertebral bodies and in the inter pubic articulation. In the freely movable joints, the surfaces are completely separated. The bones forming the articulation are expanded for greater convenience of mutual connection, covered by cartilage and enveloped by capsules of fibrous tissue. The cells lining the interior of the fibrous capsule form an imperfect membrane, the synovial membrane, which secretes a lubricating fluid. The joints are strengthened by strong fibrous bands called ligaments, which extend between the bones forming the joint. Bone. Bone constitutes the fundamental element of all the joints. In the long bones, the extremities are the parts which form the articulations. They are generally somewhat enlarged and consist of spongy, cancellous tissue with a thin coating of compact substance. In the flat bones, the articulations usually take place at the edges and in the short bones at various parts of their surfaces. The layer of compact bone which forms the joint surface and to which the articular cartilage is attached is called the articular lamella. It differs from ordinary bone tissue in that it contains no heversian canals and its lacunae are larger and have no canaliculi. The vessels of the cancellous tissue as they approach the articular lamella turn back in loops and do not perforate it. This layer is consequently denser and firmer than ordinary bone and is evidently designed to form an unyielding support for the articular cartilage. Cartilage. Cartilage is a non-vascular structure which is found in various parts of the body. In adult life, chiefly in the joints, in the parieties of the thorax and in various tubes such as the trachea and bronchi, nose and ears which require to be kept permanently open. In the fetus at an early period, the greater part of the skeleton is cartilaginous. As this cartilage is afterward replaced by bone, it is called temporary. In contradistinction to that, which remains unossified during the whole of life and is called permanent. Cartilage is divided according to its minute structure into hyaline cartilage, white fibrocartilage and yellow or elastic fibrocartilage. Hyaline cartilage. Hyaline cartilage consists of a gristly mass of a firm consistence but of considerable elasticity and pearly bluish color. Except where it coats the articular ends of bones, it is covered externally by a fibrous membrane, the paracondrium from the vessels of which it imbibes its nutritive fluids being itself destitute of blood vessels. It contains no nerves. Its intimate structure is very simple. If a thin slice be examined under the microscope, it will be found to consist of cells of a rounded or bluntly angular form lying in groups of two or more in a granular or almost homogeneous matrix. The cells when arranged in groups of two or more have generally straight outlines when they are in contact with each other and in the rest of their circumference are rounded. They consist of clear translucent protoplasm in which fine interlacing filaments and minute granules are sometimes present. Embedded in this are one or two round nuclei having the usual intranuclear network. The cells are contained in cavities in the matrix called cartilage lacunae. Around these the matrix is arranged in concentric lines as if it had been formed in successive portions around the cartilage cells. This constitutes the so-called capsule of the space. Each lacuna is generally occupied by a single cell but during the division of the cells it may contain two, four, or eight cells. The matrix is transparent and apparently without structure or else presents a dimly granular appearance like ground glass. Some observers have shown that the matrix of hyaline cartilage and especially of the articular variety after prolonged maceration can be broken up into fine fibrils. These fibrils are probably of the same nature, chemically, as the white fibers of connective tissue. It is believed by some histologists that the matrix is permeated by a number of fine channels which connect the lacunae with each other and that these canals communicate with the lymphatics of the pericondrium and thus the structure is permeated by a current of nutrient fluid. Articular cartilage, costal cartilage, and temporary cartilage are all of the hyaline variety. They present differences in the size, shape, and arrangement of their cells. In articular cartilage, which shows no tendency to ossification, the matrix is finely granular, the cells in nuclei are small and are disposed parallel to the surface in the superficial part while nearer to the bone they are arranged in vertical rows. Articular cartilages have a tendency to split in a vertical direction. In disease this tendency becomes very manifest. The free surface of articular cartilage, where it is exposed to friction, is not covered by pericondrium, although a layer of connective tissue continuous with that of the synovial membrane can be traced in the adult over a small part of its circumference. And here the cartilage cells are more or less branched and pass insensibly into the branched connective tissue corpuscles of the synovial membrane. Articular cartilage forms a thin incrust station upon the joint surfaces of the bones and its elasticity enables it to break the force of concussions while its smoothness affords ease and freedom of movement. It varies in thickness according to the shape of the articular surface on which it lies. Where this is convex, the cartilage is thickest at the center, the reverse being the case on concave articular surfaces. It appears to derive its nutriment partly from the vessels of the neighboring synovial membrane and partly from those of the bone upon which it is implanted. Toinby has shown that the minute vessels of the cancellous tissue as they approach the articular lamella dilate and form arches and then return into the substance of the bone. In costal cartilage the cells in nuclei are large and the matrix has a tendency to fibrous striation, especially in old age. In the thickest parts of the costal cartilages a few large vascular channels may be detected. This appears at first sight to be an exception to the statement that cartilage is a non-vascular tissue. But it is not so really for the vessels give no branches to the cartilage substance itself and the channels may rather be looked upon as involutions of the pericondrium. The xiphoid process and the cartilages of the nose, larynx and trachea, except the epiglottis and corniculate cartilages of the larynx which are composed of elastic fibrocartilage, resemble the costal cartilages and microscopic characteristics. The arytenoid cartilage of the larynx shows a transition from hyaline cartilage at its base to elastic cartilage at the apex. The hyaline cartilages, especially in adult and advanced life, are prone to calcify, that is to say, to have their matrix permeated by calcium salts without any appearance of true bone. The process of calcification occurs frequently in such cartilages as those of the trachea and in the costal cartilages where it may be succeeded by conversion into true bone. White fibrocartilage White fibrocartilage consists of a mixture of white fibrous tissue and cartilaginous tissue in various proportions. To the former of these constituents it owes its flexibility and toughness and to the latter its elasticity. When examined under the microscope it is found to be made up of fibrous connective tissue arranged in bundles with cartilage cells between the bundles. The cells to a certain extent resemble tendon cells but may be distinguished from them by being surrounded by a concentrically striated area of cartilage matrix and by being less flattened. The white fibrocartilages admit of arrangement into four groups, interarticular, connecting, circumferential, and stratiform. One. The interarticular fibrocartilages, menisci, are flattened fibrocartilaginous plates of a round, oval, triangular, or sickle-like form interposed between the articular cartilages of certain joints. They are free on both surfaces, usually thinner toward the center than at the circumference and held in position by the attachment of their margins and extremities to the surrounding ligaments. The synovial membranes of the joints are prolonged over them. They are found in the temporomandibular, sternoclavicular, acromioclavicular, wrist and knee joints, that is, in those joints which are most exposed to violent concussion and subject to frequent movement. Their uses are to obliterate the intervals between opposed surfaces in their various motions, to increase the depths of the articular surfaces and give ease to the gliding movements, to moderate the effects of great pressure and deaden the intensity of the shocks to which the parts may be subjected. Humphrey has pointed out that these interarticular fibrocartilages serve an important purpose in increasing the varieties of movement in a joint. Thus in the knee joint there are two kinds of motion, that is, angular movement and rotation, although it is a hinge joint in which, as a rule, only one variety of motion is permitted. The former movement takes place between the condyles of the femur and the interarticular cartilages, the latter between the cartilages and the head of the tibia. So also in the temporomandibular joint, the movements of opening and shutting the mouth take place between the fibrocartilage and the mandible, the grinding movement between the mandibular fossa and the fibrocartilage, the latter moving with the mandible. Two. The connecting fibrocartilages are imposed between the bony surfaces of those joints which admit of only slight mobility, as between the bodies of the vertebrae. They form discs which are closely adherent to the opposed surfaces. Each disc is composed of concentric rings of fibrous tissue, with cartilaginous laminae interposed, the former tissue predominating toward the circumference, the latter toward the center. Three. The circumferential fibrocartilages consist of rims of fibrocartilage which surround the margins of some of the articular cavities, for example, the glenoidal labrum of the hip and of the shoulder. They serve to deepen the articular cavities and to protect their edges. Four. The stratiform fibrocartilages are those which form a thin coating to osseous grooves in which the tendons of certain muscles glide. Small masses of fibrocartilage are also developed in the tendons of some muscles where they glide over bones, as in the tendons of the perineus longus and tibialis posterior. The distinguishing feature of cartilage chemically is that it yields on boiling a substance called chondrin, very similar to gelatin, but differing from it in several of its reactions. It is now believed that chondrin is not a simple body, but a mixture of gelatin with mucinoid substances, chief among which, perhaps, is a compound termed chondromucoid. Ligaments. Ligaments are composed mainly of bundles of white fibrous tissue placed parallel with or closely interlaced with one another and present a white, shining, silvery appearance. They are pliant and flexible so as to allow perfect freedom of movement, but strong, tough, and inextensible, so as not to yield readily to applied force. Some ligaments consist entirely of yellow elastic tissue, as the ligamenta flava, which connect together the laminate of adjacent vertebrae, and the ligamentum nuke in the lower animals. In these cases, the elasticity of the ligament is intended to act as a substitute for muscular power. The articular capsules. The articular capsules form complete envelopes for the freely movable joints. Each capsule consists of two strata, an external, stratum fibrosum, composed of white fibrous tissue and an internal, stratum synovial, which is a secreting layer and is usually described separately as the synovial membrane. The fibrous capsule is attached to the whole circumference of the articular end of each bone entering into the joint and thus entirely surrounds the articulation. The synovial membrane invests the inner surface of the fibrous capsule and is reflected over any tendons passing through the joint cavity, as the tendon of the popliteus in the knee and the tendon of the biceps brachii in the shoulder. It is composed of a thin, delicate connective tissue with branched connective tissue corpuscles. Its secretion is thick, viscid and glary, like the white of an egg and is hence termed synovia. In the fetus this membrane is said, by Toynbee, to be continued over the surfaces of the cartilages. But in the adult such a continuation is wanting, accepting at the circumference of the cartilage, upon which it encroaches for a short distance and to which it is firmly attached. In some of the joints the synovial membrane is thrown into folds which pass across the cavity. They are especially distinct in the knee. In other joints there are flattened folds subdivided at their margins into fringe-like processes which contain convoluted vessels. These folds generally project from the synovial membrane near the margin of the cartilage and lie flat upon its surface. They consist of connective tissue covered with endothelium and contain fat cells in variable quantities isolated cartilage cells. The larger folds often contain considerable quantities of fat. Closely associated with synovial membrane and therefore conveniently described in this section are the mucous sheaths of tendons and the mucous bursae. Mucous sheaths, vaginae mucosae serve to facilitate the gliding of tendons in fibro-osseous canals. Each sheath is arranged in the form of an elongated closed sac, one layer of which adheres to the wall of the canal, and the other is reflected upon the surface of the enclosed tendon. These sheaths are chiefly found surrounding the tendons of the flexor and extensor muscles of the fingers and toes as they pass through fibro-osseous canals in or near the hand and foot. Bursae mucosae are interposed between surfaces which glide upon each other. They consist of closed sacs containing a minute quantity of clear viscid fluid and may be grouped according to their situations under the headings subcutaneous, submuscular, subfacial, and subtendinous. End of section 1 Section 2 of Graze Anatomy Part 2 This is a Librevox recording. All Librevox recordings are in the public domain. For more information or to volunteer, please visit Librevox.com Here, please visit Librevox.org Recording by Morgan Scorpion Anatomy of the Human Body Part 2 by Henry Gray Development and classification of joints Movement admitted in joints 2. Development of the joints The mesoderm from which the different parts of the skeleton are formed shows at first no differentiation into masses corresponding with the individual bones. Thus continuous cause of mesoderm from the axis of the limb buds and a continuous column of mesoderm the future vertical column. The first indications of the bones and joints are circumscribed condensations of the mesoderm. These condensed parts become quantified and finally ossified to form the bones of the skeleton. The intervening non-condensed portions consist of undifferentiated mesoderm which may develop in one of three directions. It may be converted into fibrous tissue as in the case of the skull bones a synarthroidal joint being the result or it may become partly cartilaginous in which case an amphiarthroidal joint is formed. Again it may become looser in texture and a cavity ultimately appears in its midst. The cells lining the sides of this cavity form a synovial membrane and thus a diarthroidal joint is developed. The tissue surrounding the original mesodermal core forms fibrous sheaths for the developing bones i.e. periosteum and pericondrium which are continued between the ends of the bones over the synovial membrane as the capsules of the joints. These capsules are not of uniform thickness so that in them may be recognised especially strengthened bands which are described as ligaments. This however is not the only method of formation of ligaments. In some cases by modification of or derivations from the tendons surrounding the joint additional ligamentous bands are provided to further strengthen the articulations. In several of the movable joints the mesoderm which originally existed between the ends of the bones does not become completely absorbed a portion of it persists and forms an articular disc. These discs may be intimately associated in their development with the muscles surrounding the joint i.e. the menisci of the knee joint or with cartilaginous elements representatives of skeletal structures which are vestigial in human anatomy i.e. the articular disc of the sternoclavicular joint. 3. Classification of joints The articulations are divided into three classes synarthrosis or immovable amphiarthrosis or slightly immovable and diarthrosis or freely movable joints synarthrosis immovable articulations Synarthrosis include all these articulations in which the surfaces of the bones are in almost direct contact fastened together by intervening connective tissue or hyaline cartilage and in which there is no appreciable motion as in the joints between the bones of the skull accepting those of the mandible There are four varieties of synarthrosis sutura chindulacis gonphosis and synchondrosis sutura Sutura is that form of articulation where the contiguous margins of the bones are united by a thin layer of fibrous tissue it is met with only in the skull When the margins of the bones are connected by a series of processes and indentations interlocked together the articulation is termed a true suture sutura vira and of this there are three varieties sutura dentata, serata and dimbosa the margins of the bones are not in direct contact being separated by a thin layer of fibrous tissue continuous externally with the perichranium internally with the duomata the sutura dentata is so called from the tooth-like form of the projecting processes as in the suture between the parietal bones In the sutura serata the edges of the bones are serrated like the teeth of a fine saw as between the two portions of the frontal bone In the sutura dimbosa there is besides the interlocking a certain degree of bevelling of the articular surfaces so that the bones overlap one another as in the suture between the parietal and frontal bones When the articulation is formed by roughen surfaces placed in opposition with one another it is termed a false suture sutureanosa of which there are two kinds the sutura squamosa formed by the overlapping of contiguous bones by broad bevelled margins as in the squamosal suture between the temporal and parietal and the sutura harmonia where there is simple opposition of contiguous rough surfaces between the maxillae or between the horizontal parts of the palatine bones chindulacis chindulacis is that form of articulation in which a thin plate of bone is received into a cleft or fissure formed by the separation of two laminae in another bone as in the articulation of the rostrum of the sphenoid and perpendicular plate of the ethmoid with the vomar or in the reception of the latter in the fissure between the maxillae and between the palatine bones gonfosis is articulation by the insertion of a conical process into a socket this is not illustrated by any articulation between bones, properly so called but is seen in the articulations of the roots of the teeth with the alveoli of the mandible and maxillae synchondrosis where the connecting medium is cartilage the joint is termed a synchondrosis this is a temporary form of joint for the cartilage is converted into bone before adult life such joints are found between the epiphyces and bodies of long bones between the occipital and the sphenoid at and for some years after birth and between the petrus portion of the temporal and the jugular process of the occipital anthearthrosis slightly movable articulations in these articulations the contiguous bony surfaces are either connected by broad flattened discs of fibrocartilage of a more or less complex structure in the articulations between the bodies of the vertebrae or are united by an interosseous ligament as in the inferior tibiofibular articulation the first form is termed a symphysis the second a syndesmosis diarthrosis freely movable articulations this class includes the greater number of the joints in the body in a diarthrodial joint the contiguous bony surfaces are covered with articular cartilage and connected by ligaments lined by synovial membrane the joint may be divided completely or incompletely by an articular disc or meniscus the periphery of which is continuous with the fibroscapsule while its free surfaces are covered by synovial membrane the varieties of joints in this class have been determined by the kind of motion permitted in each there are two varieties in which the movement is uniaxial that is to say all movements take place around one axis in one form the ginglimus the axis is, practically speaking transverse in the other the trochoid or pivot joint it is longitudinal there are two varieties where the movement is biaxial or around two horizontal axis at right angles to each other or at any intervening axis between the two these are the condyloid and the saddle joint there is one form where the movement is polyaxial the anarthrosis or ball and socket joint and finally there are the arthrodia or gliding joints ginglimus or hinge joint in this form the articular surfaces are moulded to each other in such a manner as to permit motion only in one plane forward and backward the extent of motion at the same time being considerable the direction in which the distal bone takes in this motion is seldom in the same plane as of the proximal bone there is usually a certain amount of deviation from the straight line during flexion the articular surfaces are connected together by strong collateral ligaments which form their chief bond of union the best examples of ginglimus are the interphalangeal joints and the joint between the humerus and ulna the knee and ankle joints are less typical as they allow a slight degree of rotation or of side to side movement in certain positions of the limb trochoid or pivot joint articulatio trochoidea rotary joint where the movement is limited to rotation the joint is formed by a pivot like process turning within a ring or a ring on a pivot the ring being formed partly of bone partly of ligament in the proximal radio ulna articulation the ring is formed by the radial notch of the ulna and the annular ligament here the head of the radius rotates within the ring in the articulation of the odontoid process of the axis with the atlas the ring is formed in front by the anterior arch and behind by the transverse ligament of the atlas here the ring rotates around the odontoid process condyloid articulation articulatio ellipsoidea in this form of joint an ovoid articular surface or condyle is received into an elliptical cavity in such a manner as to permit a flexion extension, adduction abduction and circumduction but no axial rotation the wrist joint is an example of this form of articulation articulation by reciprocal reception articulatio cellaris saddle joint in this variety the opposing surfaces are reciprocally concave convex the movements are the same as in the form that is to say flexion extension, adduction, abduction and circumduction are allowed but no axial rotation the best example of this form is the carpometacarpal joint of the thumb anarthrosis ball and socket joints anarthrosis is a joint in which the distal bone is capable of motion around an indefinite number of axes which have one common centre it is formed by the reception of a globular head into a cup-like cavity hence the name ball and socket examples of this form of articulation are found in the hip and shoulder arthrodia, gliding joints is a joint which admits of only gliding movement it is formed by the opposition of plane surfaces or one slightly concave the other slightly convex the amount of motion between them being limited by the ligaments or osseous processes surrounding the articulation it is the form present in the joints between the articular processes of the vertebrae, the carpal joints accept that of the capitate with the navicular and lunate and the tarsal joints with the exception of that between the talus and the navicular end of section 2 section 3 of Grey's Anatomy part 2 this is a LibriVox recording all LibriVox recordings are in the public domain for more information or to volunteer please visit LibriVox.org recording by Morgan Scorpion anatomy of the human body part 2 by Henry Grey articulations of the vertebral column 5 articulations of the trunk a. articulations of the vertebral column these may be divided into the following groups 1 of the vertebral column 2 of the atlas with the axis 3 of the vertebral column with the cranium 4 of the mandible 5 of the ribs with the vertebrae 6 of the cartilages of the ribs with the sternum and with each other 7 of the sternum 8 of the vertebral column with the pelvis 9 of the pelvis articulations of the vertebral column the articulations of the vertebral column consist of 1 a series of amphiarthroidal joints between the vertebral bodies and 2 a series of diarthrodial joints between the vertebral arches 1 articulations of the vertebral bodies inter-central ligaments the articulations between the bodies of the vertebrae are amphiarthroidial joints and the individual vertebrae vertebrae move only slightly on each other. When, however, this slight degree of movement between the pairs of bones take place in all the joints of the vertebral column, the total range of movement is very considerable. The ligaments of these articulations are the following, the anterior longitudinal, the posterior longitudinal, the intervertebral fibrocartilages, the anterior longitudinal ligament, ligamentum longitudinali anterior, anterior common ligament. The anterior longitudinal ligament is a broad and strong band of fibres which extends along the anterior surfaces of the bodies of the vertebrae from the axis to the sacrum. It is broader below than above, thicker in the thoracic than in the cervical and lumbar regions, and somewhat thicker opposite the bodies of the vertebrae than opposite the intervertebral fibrocartilages. It is attached above to the body of the axis, where it is continuous with the anterior atlantoaxial ligament, and extends down as far as the upper part of the front of the sacrum. It consists of dense longitudinal fibres, which are intimately adherent to the intervertebral fibrocartilages and the prominent margins of the vertebrae, but not to the middle parts of the bodies. In the latter situation the ligament is stick and serves to fill up the concavities of the anterior surfaces, and to make the front of the vertebral column more even. It is composed of several layers of fibres which vary in length, but are closely interlaced with each other. The most superficial fibres are the longest and extend between four or five vertebrae. A second, subjacent set extends between two or three vertebrae while a third set, the shortest and deepest, reaches from one vertebra to the next. At the sides of the bodies the ligament consists of a few short fibres which pass from one vertebra to the next, separated from the concavities of the vertebral bodies by oval apertures for the passage of vessels. The posterior longitudinal ligament Ligamentum longitudinali posterius posterior common ligament The posterior longitudinal ligament is situated within the vertebral canal and extends along the posterior surfaces of the bodies of the vertebrae, from the body of the axis, where it is continuous with the membranotectoria, to the sacrum. It is broader above than below and thicker in the thoracic than in the cervical and lumbar regions. In the situation of the intervertebral cartilages and contiguous margins of the vertebrae, where the ligament is more intimately adherent, it is broad, and in the thoracic and lumbar regions presents a series of dentations with intervening concave margins. But it is narrow and thick over the centres of the bodies, from which it is separated by the massive vertebral veins. The ligament is composed of smooth, shining, longitudinal fibres, denser and more compact than those of the anterior ligament, and consists of superficial layers occupying the interval between three or four vertebrae, and deeper layers which extend between adjacent vertebrae. The intervertebral fibrocartilages Fibrocartilagines intervertebralis intervertebral discs The intervertebral fibrocartilages are interposed between the adjacent surfaces of the bodies of the vertebrae, from the axis to the sacrum, and form the chief bonds of connection between the vertebrae. They vary in shape, size and thickness, in different parts of the vertebral column. In shape and size they correspond with the surfaces of the bodies between which they are placed, except in the cervical region, where they are slightly smaller from side to side than the corresponding bodies. In thickness they vary not only in the different regions of the column, but in different parts of the same fibrocartilage. They are thicker in front than behind in the cervical and lumbar regions, and thus contribute to the anterior convexities of these parts of the column, while they are of nearly uniform thickness in the thoracic region, the anterior concavity of this part of the column being almost entirely owing to the shape of the vertebral bodies. The intervertebral fibrocartilages constitute about one fourth of the length of the vertebral column, exclusive of the first two vertebrae, but this amount is not equally distributed between the various bones, the cervical and lumbar portions having, in proportion to their length, a much greater amount than the thoracic region, with the result that these parts possess greater pliancy and freedom of movement. The intervertebral fibrocartilages are adherent by their surfaces to thin layers of high-lying cartilage which cover the upper and under surfaces of the bodies of the vertebrae. In the lower cervical vertebrae however, small joints lined by synovial membrane are occasionally present between the upper surfaces of the bodies and the margins of the fibrocartilages on either side. By their circumferences the intervertebral fibrocartilages are closely connected in front to the anterior and behind to the posterior longitudinal ligaments. In the thoracic region they are joined laterally by means of the interarticular ligaments to the heads of those ribs which articulate with the two vertebrae. Structure of the intervertebral fibrocartilages. Each is composed at its circumference of lamini of fibrous tissue and fibrocartilage forming the annulus fibrosis, and at its centre of a soft pulpy, highly elastic substance of a yellowish colour which projects considerably above the surrounding level when the disc is divided horizontally. This pulpy substance, nucleus pulposis, especially well developed in the Lamber region, is the remains of the notochord. The lamini are arranged concentrically. The outermosts consist of ordinary fibrous tissue, the others of white fibrocartilage. The lamini are not quite vertical in their direction. Those near the circumference being curved outward and closely approximated, while those nearest the centre curve in the opposite direction and are somewhat more widely separated. The fibres of which each lamina is composed are directed, for the most part, obliquely from above downward. The fibres of adjacent lamini passing in opposite directions and varying in every layer, so that the fibres of one layer are directed across those of another, like the limbs of the letter X. This lamina arrangement belongs to about the outer half of each fibrocartilage. The pulpy substance presents no such arrangement, and consists of a fine fibrous matrix containing angular cells united to form a reticular structure. The intervertebral fibrocartilages are important shock absorbers. Under pressure the highly elastic nucleus pulposis becomes flatter and broader and pushes the more resistant fibrous lamini outward in all directions. 2. Articulations of Vertible Arches The joints between the articular processes of the vertebrae belong to the arthrodial variety and are enveloped by capsules lined by synovial membranes, while the lamini, spinous and transverse processes are connected by the following ligaments. The ligamenta flavour, the ligamentum nucae, the supraspinal, the interspinal, the intertransverse, the articular capsules, capsuli articulares, capsular ligaments. The articular capsules are thin and loose and are attached to the margins of the articular process of adjacent vertebrae. They are longer and looser in the cervical than in the thoracic and lumbar regions. 3. The ligamenta flavour, the ligamenta subflavour. The ligamenta flavour connect the lamini of adjacent vertebrae from the axis to the first segment of the sacrum. They are best seen from the interior of the vertebral canal, when looked at from the outer surface they appear short, being overlapped by the lamini. Each ligament consists of two lateral portions which commence one on either side of the roots of the articular processes, and extend backwards to the point where the lamini meet to form the spinous process. The posterior margins of the two portions are in contact, and to a certain extent united, slight intervals being left for the passage of small vessels. Each consists of yellow elastic tissue, the fibres of which, almost perpendicular in direction, are attached to the anterior surface of the lamina above, some distance from its inferior margin, and to the posterior surface and upper margin of the lamina below. In the cervical region the ligaments are thin, but broad and long. They are thicker in the thoracic region, and thickest in the lumbar region. Their marked elasticity serves to preserve the upright posture, and to assist the vertebral column in resuming it after flexion. The supraspinal ligament, ligamentum supraspinale, supraspinus ligament. The supraspinal ligament is a strong fibrous cord which connects together the apices of the spinous processes from the seventh cervical vertebra to the sacrum, at the points of attachment to the tips of the spinous processes, fibrocartilage is developed in the ligament. It is thicker and broader in the lumbar than in the thoracic region, and intimately blended in both situations with the neighbouring fascia. The most superficial fibres of this ligament extend over three or four vertebrae, those more deeply seated pass between two or three vertebrae, while the deepest connect the spinous processes of the neighbouring vertebrae. Between the spinous processes it is continuous with the interspinal ligaments. It is continued upward to the external occipital protuberance and medial nucol line as the ligamentum nucae. The ligamentum nucae. The ligamentum nucae is a fibrous membrane which, in the neck, represents the supraspinal ligaments of the lower vertebrae. It extends from the external occipital protuberance and the medial nucol line to the spinous process of the seventh cervical vertebrae. From its anterior border a fibrous lamina is given off, which is attached to the posterior tubercle of the atlas, and to the spinous processes of the cervical vertebrae, and forms a septum between the muscles on either side of the neck. In man it is merely the rudiment of an important elastic ligament, which, in some of the lower animals, serves to sustain the weight of the head. The interspinal ligaments. Ligamenta interspinalia interspinous ligaments. The interspinal ligaments, thin and membranous, connect adjoining spinous processes and extend from the root to the apex of each process. They meet the ligamenta flavour in front and the supraspinal ligament behind. They are narrow and elongated in the thoracic region, broader, thicker and quadrilateral in form in the lumbar region, and only slightly developed in the neck. The intertransverse ligaments. Ligamenta intertransversaria. The intertransverse ligaments are interposed between the transverse processes. In the cervical region they consist of a few irregular, scattered fibres. In the thoracic region they are rounded cords, intimately connected with the deep muscles of the back. In the lumbar region they are thin and membranous. Movements. The movements permitted in the vertebral column are flexion, extension, lateral movement, circumduction and rotation. In flexion or movement forward the anterior longitudinal ligament is relaxed and the intervertebral fibrocartilages are compressed in front. While the posterior longitudinal ligament, the ligamenta flavour and the inter and supraspinal ligaments are stretched, as well as the posterior fibres of the intervertebral fibrocartilages. The interspaces between the laminae are widened and the inferior articular processes glide upward, upon the superior articular processes of the subjacent vertebrae. Flexion is the most extensive of all the movements of the vertebral column and is freest in the lumbar region. In extension or movement backward, an exactly opposite disposition of the parts takes place. The movement is limited by the anterior longitudinal ligament and by the approximation of the spinous processes. It is freest in the cervical region. In lateral movement the sides of the intervertebral fibrocartilages are compressed, the extent of motion being limited by the resistance offered by the surrounding ligaments. This movement may take place in any part of the column, but is freest in the cervical and lumbar regions. Circumduction is very limited and is merely a succession of the preceding movements. Rotation is produced by the twisting of the intervertebral fibrocartilages. This, although only slight between any two vertebrae, allows of a considerable extent of movement when it takes place in the whole length of the column. The front of the upper part of the column being turned to one or other side. This movement occurs to a slight extent in the cervical region, is freer in the upper part of the thoracic region and absent in the lumbar region. The extent and variety of the movements are influenced by the shape and direction of the articular surfaces. In the cervical region the upward inclination of the superior articular surfaces allows of free flexion and extension. Extension can be carried farther than flexion, at the upper end of the region it is checked by the locking of the posterior edges of the superior atlantal facets in the contolloid foci of the occipital bone. At the lower end it is limited by a mechanism whereby the inferior articular processes of the seventh cervical vertebrae slip into grooves behind and below the superior articular processes of the first thoracic. Flexion is arrested just beyond the point where the cervical convexity is straightened. The movement is checked by the opposition of the projecting lower lips of the bodies of the vertebrae with the shelving surfaces on the bodies of the subjacent vertebrae. Lateral flexion and rotation are free in the cervical region, they are however always combined. The upward and medial inclinations of the superior articular surfaces impart a rotary movement during lateral flexion, while pure rotation is prevented by the slight medial slope of these surfaces. In the thoracic region, notably in its upper part, all the movements are limited in order to reduce interference with respiration to a minimum. The almost complete absence of an upward inclination of the superior articular surfaces prohibits any marked flexion while extension is checked by the contact of the inferior articular margins with the laminae, and the contact of the spinous processes with one another. The mechanism between the seventh cervical and the first thoracic vertebrae, which limits extension of the cervical region, will also serve to limit flexion of the thoracic region when the neck is extended. Rotation is free in the thoracic region, the superior articular processes are segments of a cylinder whose axis is in the mid-ventral line of the vertebral bodies. The direction of the articular facets would allow a free lateral flexion, but the movement is considerably limited in the upper part of the region by the resistance of the ribs and sternum. In the lumbar region, flexion and extension are free. Flexion can be carried farther than extension, and is possible to just beyond the straightening of the lumbar curve. It is therefore greatest at the lowest part where the curve is sharpest. The inferior articular facets are not in close opposition with the superior facets of the subjacent vertebrae, and on this account a considerable amount of lateral flexion is permitted. For the same reason, a slight amount of rotation can be carried out, but this is so soon checked by the interlocking of the articular surfaces that it is negligible. The principal muscles which produce flexion are the sternocleidomastoidaeus, longest capitis, and longest collie, the scalene, the abdominal muscles, and the psoas major. Extension is produced by the intrinsic muscles of the back, assisted in the neck by the splenius, semi-spinalis, dorsi and cervicus, and the multifidus. Lateral motion is produced by the intrinsic muscles of the back by the splenius, the scalene, the quadratus lumborum, and the psoas major. The muscles of one side only acting, and rotation by the action of the following muscles of one side only. Vis, the sternocleidomastoidaeus, the longest capitis, the scalene, the multifidus, the semi-spinalis capitis, and the abdominal muscles. End of section 3 Section 4 of Gray's Anatomy, Part 2 This is a LibriVox recording. All LibriVox recordings are in the public domain. For more information or to volunteer, please visit LibriVox.org. Recording by Morgan Scorpion. Anatomy of the Human Body, Part 2 by Henry Gray Articulation of Atlas with Epistrophias of Vertebral Column with Cranium 5b. Articulation of the Atlas with the Epistrophias or Axis Articulatio Atlanta Epistrophica The articulation of the Atlas with the Axis is of a complicated nature, comprising no fewer than four distinct joints. There is a pivot articulation between the odontoid process of the Axis and the ring formed by the anterior arch and the transverse ligament of the Atlas. Here there are two joints, one between the posterior surface of the anterior arch of the Atlas and the front of the odontoid process, the other between the anterior surface of the ligament and the back of the process. Between the articular processes of the two bones, there is on either side an arthrodial or gliding joint. The ligaments connecting these bones are two articular capsules, the anterior atlantoaxial, the posterior atlantoaxial, the transverse. The Articular Capsules Capsuli articularis capsular ligaments The Articular Capsules are thin and loose and connect the margins of the lateral masses of the Atlas with those of the posterior articular surfaces of the Axis. Each is strengthened at its posterior and medial part by an accessory ligament, which is attached below to the body of the Axis near the base of the odontoid process and above to the lateral mass of the Atlas near the transverse ligament, the anterior atlantoaxial ligament. This ligament is a strong membrane fixed above to the lower border of the anterior arch of the Atlas below to the front of the body of the Axis. It is strengthened in the middle by a rounded cord, which connects the tubercle on the anterior arch of the Atlas to the body of the Axis and is a continuation upward of the anterior longitudinal ligament. The ligament is in relation, in front, with the longy capitis, the posterior atlantoaxial ligament. This ligament is a broad thin membrane attached above to the lower border of the posterior arch of the Atlas below to the upper edges of the lamini of the Axis. It supplies the place of the ligament of flavour and is in relation behind with the obliquy capitis inferioris. The transverse ligament of the Atlas ligamentum transversum atlantis. The transverse ligament of the Atlas is a thick, strong band which arches across the ring of the Atlas and retains the odontoid process in contact with the anterior arch. It is concave in front, convex behind, broader and thicker in the middle than at the ends and firmly attached on either side to a small tubercle on the medial surface of the lateral mass of the Atlas. As it crosses the odontoid process, a small fasciculus, cruise superioris, is prolonged upward and another, cruise inferioris, downward, from the superficial or posterior fibres of the ligament. The former is attached to the basilar part of the occipital bone, in close relation with the membrana tectoria. The latter is fixed to the posterior surface of the body of the Axis. Hence, the whole ligament is named the cruciate ligament of the Atlas. The transverse ligament divides the ring of the Atlas into two unequal parts. Of these, the posterior and larger serves for the transmission of the medullus spinalis and its membranes and the accessory nerves. The anterior and smaller contains the odontoid process. The neck of the odontoid process is constricted where it is embraced posteriorly by the transverse ligament, so that this ligament suffices to retain the odontoid process in position after all the other ligaments have been divided. Synovial membranes. There is a synovial membrane for each of the four joints. The joint cavity between the odontoid process and the transverse ligament is often continuous with those of the atlantooccipital articulations. Movements. The opposed articular surfaces of the Atlas and Axis are not reciprocally curved. Both surfaces are convex in their long axes. When therefore the upper facet glides forward on the lower, it also descends. The fibres of the articular capsule are relaxed in a vertical direction and will then permit of movement in an antero-posterior direction. By this means a shorter capsule suffices and the strength of the joint is materially increased. Note 67. Corner. The physiology of the atlanto-axial joints. Journal of Anatomy and Physiology. Volume 41. States that the movements which take place at these articulations are of a complex nature. The first part of the movement is an eccentric or asymmetrical one. The atlanto-axial joint of the side to which the head is moved is fixed, or practically fixed, by the muscles of the neck and forms the centre of the movement, while the opposite atlantal facet is carried downward and forward on the corresponding axial facet. The second part of the movement is centric and symmetrical. The odontoid process forming the axis of the movement. End of note. This joint allows the rotation of the atlas and, with it, the skull upon the axis, the extent of rotation being limited by the aila ligaments. The principal muscles by which these movements are produced are the sternocleidomastoid deus and semispinalis capitis of one side, acting with the longest capitis, splenius, longissimus capitis, rectus capitis posterior major, and obliquy capitis superior and inferior of the other side. Five C. Articulations of the vertical column with the cranium. The ligaments connecting the vertical column with the cranium may be divided into two sets, those uniting the atlas with the occipital bone, and those connecting the axis with the occipital bone. Articulation of the atlas with the occipital bone. Articulatio atlantooccipitalis. The articulation between the atlas and the occipital bone consists of a pair of congeloid joints. The ligaments connecting the bones are two articular capsules, the anterior atlantooccipital membrane, the posterior atlantooccipital membrane, two lateral atlantooccipital. The articular capsules. Capsuli articulareis capsula ligaments. The articular capsules surround the condyles of the occipital bone, and connect them with the articular processes of the atlas. They are thin and loose. The anterior atlantooccipital membrane. Membrana atlantooccipitalis anterior. Anterior atlantooccipital ligament. The anterior atlantooccipitalis membrane is broad and composed of densely woven fibres, which pass between the anterior margin of the forearm and magnum above, and the upper border of the anterior arch of the atlas below. Laterally it is continuous with the articular capsules. In front it is strengthened in the middle line by a strong rounded cord, which connects the basilar part of the occipital bone to the tubercle on the anterior arch of the atlas. The membrane is in relation in front with the recticupitis anterioris, behind with the alar ligaments. The posterior atlantooccipital membrane. Membrana atlantooccipitalis posterior. Posterior atlantooccipital ligament. The posterior atlantooccipital membrane, broad but thin, is connected above to the posterior margin of the forearm and magnum below to the upper border of the posterior arch of the atlas. On either side this membrane is defective below. Over the groove for the vertebral artery, and forms with this groove an opening for the entrance of the artery and the exit of the suboccipital nerve. The free border of the membrane, arching over the artery and nerve, is sometimes ossified. The membrane is in relation, behind with the recticupitis posterioris minoris and obliquicupitis superioris, in front with the duomata of the vertebral canal, to which it is intimately adherent. The lateral ligaments. The lateral ligaments are thickened portions of the articular capsules, reinforced by bundles of fibrous tissue, and are directed obliquely upward and medial wood. They are attached above to the jugular processes of the occipital bone, and below to the bases of the transverse processes of the atlas. Sonovial membranes. There are two sonovial membranes, one lining each of the articular capsules. The joints frequently communicate with that between the posterior surface of the odontoid process and the transverse ligament of the atlas. Movements. The movements permitted in this joint are A, flexion and extension, which give rise to the ordinary forward and backward nodding of the head, and B, slight lateral motion to one or other side. Flexion is produced mainly by the action of the longicupitis and recticupitis anterioris, extension by the recticupitis posterioris major and minor, the obliquous superior, the semispinalis capitis, splenius capitis, sonoclydomastodeus, and upper fibres of the trapezius. The recti-lateralis are concerned in the lateral movement assisted by the trapezius, splenius capitis, semispinalis capitis, and the sternoclydomastodeus of the same side, all acting together. Ligaments connecting the axis with the occipital bone. The membrane tectoria to ailer, the apical odontoid. The membrane tectoria, occipitoexial ligament. The membrane tectoria is situated within the vertebral canal. It is a broad strong band which covers the odontoid process and its ligaments, and appears to be a prolongation upward of the posterior longitudinal ligament of the vertebral column. It is fixed below to the posterior surface of the body of the axis, and, expanding as it ascends, is attached to the basilar groove of the occipital bone in front of the foramen magnum, where it blends with the cranial duomata. Its anterior surface is in relation with the transverse ligament of the atlas, and its posterior surface with the duomata. The ailer ligaments. Ligamentia allaria, odontoid ligaments. The ailer ligaments are strong rounded cords which arise one on either side of the upper part of the odontoid process, and, passing obliquely upward and lateral wood, are inserted into the rough depressions on the medial sides of the condyles of the occipital bone. In the triangular interval between these ligaments is another fibrous cord, the apical odontoid ligament, which extends from the tip of the odontoid process to the anterior margin of the foramen magnum, being intimately blended with the deep portion of the anterior atlanta occipital membrane and superior cruce of the transverse ligament of the atlas. It is regarded as a rudimentary intervertebral fibrocartilage, and in it traces of the notochord may persist. The ailer ligaments limit rotation of the cranium, and therefore receive the name of check ligaments. In addition to the ligaments which unite the atlas and axis to the skull, the ligamentum nuci must be regarded as one of the ligaments connecting the vertebral column with the cranium. End of Section 4. Section 5 of Gray's Anatomy, Part 2. This is a LibriVox recording. All LibriVox recordings are in the public domain. For more information or to volunteer, please visit LibriVox.org. Recording by Leanne Howlett. Anatomy of the Human Body, Part 2 by Henry Gray. Articulation of the Mandible. 5D, Articulation of the Mandible. Articulation, Mandibularis. Temporomandibular, Articulation. This is a Jingle Mow Arthrodial Joint. The parts entering into its formation on either side are the anterior part of the mandibular fossa of the temporal bone and the articular tubercle above and the condyle of the mandible below. The ligaments of the joint are the following. The articular capsule, the sphenomandibular, the temporomandibular, the articular disc, the stylomandibular, the articular capsule, capsular, articularis, capsular ligament. The articular capsule is a thin loose envelope attached above to the circumference of the mandibular fossa and the articular tubercle immediately in front, below to the neck of the condyle of the mandible. The temporomandibular ligament, ligamentum, temporomandibular, external lateral ligament. The temporomandibular ligament consists of two short narrow fasciculi, one in front of the other attached above to the lateral surface of the zygomatic arch and to the tubercle on its lower border, below to the lateral surface and posterior border of the neck of the mandible. It is broader above than below and its fibers are directed obliquely downward and backward. It is covered by the parotid gland and by the integument. The sphenomandibular ligament, ligamentum, sphenomandibular, internal lateral ligament. The sphenomandibular ligament is a flat thin band which is attached above to the spina angularus of the sphenoid bone and becoming broader as it descends is fixed to the lingula of the mandibular foramen. Its lateral surface is in relation above with the pterogoidus externus. Lower down it is separated from the neck of the condyle by the internal maxillary vessels. Still lower, the inferior alveolar vessels and nerve and the lobule of the parotid gland lie between it and the ramus of the mandible. Its medial surface is in relation with the pterogoidus internus. The articular disc, discus articularis, interarticular fibrocartilage, articular meniscus. The articular disc is a thin oval plate placed between the condyle of the mandible and the mandibular fossa. Its upper surface is concavo convex from before backward to accommodate itself to the form of the mandibular fossa and the articular tubercle. Its under surface, in contact with the condyle, is concave. Its circumference is connected to the articular capsule and in front to the tendon of the pterogoidus externus. It is thicker at its periphery, especially behind than at its center. The fibers of which it is composed have a concentric arrangement, more apparent at the circumference than at the center. It divides the joint into two cavities, each of which is furnished with synovial membrane. The synovial membranes. The synovial membranes, two in number, are placed one above and the other below the articular disc. The upper one, the larger and looser of the two, is continued from the margin of the cartilage covering the mandibular fossa and articular tubercle onto the upper surface of the disc. The lower one passes from the under surface of the disc to the neck of the condyle, being prolonged a little farther downward behind than in front. The articular disc is sometimes perforated in its center and the two cavities then communicate with each other. The stylo mandibular ligament. Ligamentum stylo mandibular stylo maxillary ligament. The stylo mandibular ligament is a specialized band of the cervical fascia, which extends from near the apex of the styloid process of the temporal bone to the angle and posterior border of the ramus of the mandible between the masseter and pterogoidius and ternus. This ligament separates the parotid from the submaxillary gland and from its deep surface some fibers of the stylo glosses take origin. Although classed among the ligaments of the temporal mandibular joint, it can only be considered as accessory to it. The nerves of the temporal mandibular joint are derived from the auriculotemporal and masseteric branches of the mandibular nerve. The arteries from the superficial temporal branch of the external carotid. Movements. The movements permitted in this articulation are extensive. Thus the mandible may be depressed or elevated or carried forward or backward. A slight amount of side-to-side movement is also permitted. It must be borne in mind that there are two distinct joints in this articulation, one between the condyle in the articular disc and another between the disc and the mandibular fossa. When the mouth is but slightly open as during ordinary conversation, the movement is confined to the lower of the two joints. On the other hand, when the mouth is open more widely, both joints are concerned in the movement. In the lower joint the movement is of a hinge-like character, the condyle moving around a transverse axis on the disc, while in the upper joint the movement is of a gliding character, the disc together with the condyle gliding forward onto the articular tubercle around an axis which passes through the mandibular foramina. These two movements take place simultaneously. The condyle and disc move forward on the eminence and at the same time the condyle revolves on the disc. In shutting the mouth the reverse action takes place, the disc glides back carrying the condyle with it, and this at the same time moves back to its former position. When the mandible is carried horizontally forward as in protruding the lower incisor teeth in front of the upper, the movement takes place principally in the upper joint, the disc and the condyle gliding forward on the mandibular fossa and articular tubercle. The grinding or chewing movement is produced by one condyle with its disc gliding alternately forward and backward, while the other condyle moves simultaneously in the opposite direction. At the same time the condyle undergoes a vertical rotation on the disc. One condyle advances and rotates, the other condyle recedes and rotates, and alternates succession. The mandible is depressed by its own weight, assisted by the platysma, the digastricus, the mylohyoidius, and the geniohyoidius. It is elevated by the masseter, pterogoidius internus, and the anterior part of the temporalis. It is drawn forward by the simultaneous action of the pterogoidii internus and externus, the superficial fibers of the masseter and the anterior fibers of the temporalis, and backward by the deep fibers of the masseter and the posterior fibers of the temporalis. The grinding movement is caused by the alternate action of the pterogoidii of either side. End of Section 5, Recording by Leanne Howlett. Section 6 of Grey's Anatomy Part 2. This is a LibriVox recording. All LibriVox recordings are in the public domain. For more information or to volunteer, please visit LibriVox.org. Recording by Leanne Howlett. Anatomy of the Human Body, Part 2 by Henry Gray. 5e. The articulations of the ribs with the vertebral column may be divided into two sets, one connecting the heads of the ribs with the bodies of the vertebrae, another uniting the necks and tubercles of the ribs with the transverse processes. 1. Articulations of the heads of the ribs. Articulations, capitulorum, costocentral articulations. These constitute a series of gliding or arthrodial joints and are formed by the articulation of the heads of the typical ribs with the facets on the contiguous margins of the bodies of the thoracic vertebrae and with the intervertebral fibrocartilages between them. The first 10th, 11th, and 12th ribs each articulate with a single vertebra. The ligaments of the joints are the articular capsule, the radiate, the interarticular, the articular capsule, capsular articularis, capsular ligament. The articular capsule surrounds the joint being composed of short, strong fibers connecting the head of the rib with the circumference of the articular cavity formed by the intervertebral fibrocartilage and the adjacent vertebrae. It is most distinct at the upper and lower parts of the articulation. Some of its upper fibers pass through the intervertebral foramen to the back of the intervertebral fibrocartilage while its posterior fibers are continuous with the ligament of the neck of the rib. The radiate ligament, ligamentum, capituli, costi, radiatum, anterior, costo-vertebral, or stellate ligament. The radiate ligament connects the anterior part of the head of each rib with the sides of the bodies of two vertebrae and the intervertebral fibrocartilage between them. It consists of three flat fasciculi which are attached to the anterior part of the head of the rib just beyond the articular surface. The superior fasciculus ascends and is connected with the body of the vertebrae above. The inferior one descends to the body of the vertebra below. The middle one, the smallest and least distinct, is horizontal and is attached to the intervertebral fibrocartilage. The radiate ligament is in relation in front with the thoracic ganglia of the sympathetic trunk, the pleura, and on the right side with the azygos vein behind with the interarticular ligament and synovial membranes. In the case of the first rib, this ligament is not divided into three fasciculi, but its fibers are attached to the body of the last cervical vertebra, as well as to that of the first thoracic. In the articulations of the heads of the 10th, 11th, and 12th ribs, each of which articulates with a single vertebra, the tri-radiate arrangement does not exist. But the fibers of the ligament in each case are connected to the vertebra above, as well as to that with which the rib articulates. The interarticular ligament, ligamentum capituli, costi interarticular. The interarticular ligament is situated in the interior of the joint. It consists of a short band of fibers flattened from above downward, attached by one extremity to the crest separating the two articular facets on the head of the rib and by the other to the intervertebral fibrocartilage. It divides the joint into two cavities. In the joints of the first, 10th, 11th, and 12th ribs, the interarticular ligament does not exist. Consequently, there is but one cavity in each of these articulations. This ligament is the homologue of the ligamentum congegal, present in some mammals and uniting the heads of opposite ribs across the back of the intervertebral fibrocartilage. Sinovial membranes. There are two sinovial membranes in each of the articulations where an interarticular ligament exists, one above and one below this structure, but only one in those joints where there are single cavities. 2. Costotransverse articulations. Articulations costotranverserae. The articular portion of the tubercle of the rib forms with the articular surface on the adjacent transverse process on an arthrodial joint. In the 11th and 12th ribs, this articulation is wanting. The ligaments of the joint are the articular capsule, the articular capsule, the anterior costotransverse, the posterior costotransverse, the ligament of the neck of the rib, the ligament of the tubercle of the rib, the articular capsule, capsula articularis, capsular ligament. The articular capsule is a thin membrane attached to the circumferences of the articular surfaces and lined by a sinovial membrane. The anterior costotransverse ligament, ligamentum costotranversarium enterius, anterior superior ligament. The anterior costotransverse ligament is attached below to the sharp crest on the upper border of the neck of the rib and passes obliquely upward and lateralward to the lower border of the transverse process immediately above. It is in relation in front with the intercostal vessels and nerves. Its medial border is thickened and free and bounds an aperture which transmits the posterior branches of the intercostal vessels and nerves. Its lateral border is continuous with a thin aponeurosis which covers the intercostalus externus. The first rib has no anterior costotransverse ligament. A band of fibers, the lumbocostal ligament in series with the anterior costotransverse ligaments, connects the neck of the twelfth rib to the base of the transverse process of the first lumbar vertebra. It is merely a thickened portion of the posterior layer of the lumbodorsal fascia. The posterior costotransverse ligament, ligamentum costotranversarium posterioris. The posterior costotransverse ligament is a feeble band which is attached below to the neck of the rib and passes upward and medialward to the base of the transverse process and lateral border of the inferior articular process of the vertebra above. The ligament of the neck of the rib, ligamentum coli costi middle costotransverse or enterosius ligament. The ligament of the neck of the rib consists of short but strong fibers connecting the rough surface on the back of the neck of the rib with the anterior surface of the adjacent transverse process. A rudimentary ligament may be present in the case of the eleventh and twelfth ribs. The ligament of the tubercle of the rib, ligamentum tuberculi costi posterior costotransverse ligament. The ligament of the tubercle of the rib is a short but thick and strong fasciculus which passes obliquely from the apex of the transverse process to the rough nonarticular portion of the tubercle of the rib. The ligaments attached to the upper ribs ascend from the transverse processes. They are shorter and more oblique than those attached to the inferior ribs which descend slightly. Movements. The heads of the ribs are so closely connected to the bodies of the vertebrae by the radiate and interarticular ligaments that only slight gliding movements of the articular surfaces on one another can take place. Similarly, the strong ligaments binding the necks and tubercles of the ribs to the transverse processes limit the movements of the costotransverse joints to slight gliding, the nature of which is determined by the shape and direction of the articular surfaces. In the upper six ribs, the articular surfaces on the tubercles are oval in shape and convex from above downward. They fit into corresponding concavities on the anterior surfaces of the transverse processes so that upward and downward movements of the tubercles are associated with the rotation of the rib neck on its long axis. In the seventh, eight, ninth, and tenth ribs, the articular surfaces on the tubercles are flat and are directed obliquely downward, medial, and backward. The surfaces with which they articulate are placed on the upper margins of the transverse processes. When, therefore, the tubercles are drawn up, they are at the same time carried backward in medial word. The two joints, costocentral and costotransverse, move simultaneously and in the same directions. The total effect being that the neck of the rib moves as if on a single joint, of which the costocentral and costotransverse articulations form the ends. In the upper six ribs, the neck of the rib moves but slightly upward and downward. Its chief movement is one of rotation around its own long axis, rotation backward being associated with depression, rotation forward with elevation. In the seventh, eighth, ninth, and tenth ribs, the neck of the rib moves upward, backward, and medial word, or downward, forward, and lateral word. Very slight rotation accompanies these movements. End of Section 6, Recording by Leanne Howlett. Section 7 of Grey's Anatomy, Part 2. This is a LibriVox recording. All LibriVox recordings are in the public domain. For more information or to volunteer, please visit LibriVox.org. Recording by Alistair Lord. Anatomy of the Human Body, Part 2 by Henry Gray. Sternocostal articulations and articulation of manubrium and body of sternum. Sternocostal articulations. Articulation sternocotals. Costosternal articulations. The articulations of the cartilages of the true ribs with the sternum are arthrodial joints with the exception of the first in which the cartilage is directly united with the sternum and which is therefore a synarthrodial articulation. The ligaments connecting them are the articular capsules, the interarticular sternocostal, the radiate sternocostal, and the costosyfoid. The articular capsules, capsulae articularis capsular ligaments. The articular capsules surround the joints between the cartilages of the true ribs and the sternum. They are very thin, intimately blended with the radiate sternocostal ligaments and strengthened at the upper and lower parts of the articulations by a few fibres which connect the cartilages to the side of the sternum. The radiate sternocostal ligaments, ligamenta sternocostaliate radiata, chondro sternal or sternocostal ligaments. These ligaments consist of broad and thin membranous bands that radiate from the front and back of the sternal ends of the cartilages of the true ribs to the anterior and posterior surfaces of the sternum. They are composed of fasciculi, which pass in different directions. The superior fasciculi ascend obliquely, the inferior fasciculi descend obliquely, and the middle fasciculi run horizontally. The superficial fibres are the longest. They intermingle with the fibres of the ligaments above and below them, with those of the opposite side and in front with the tenderness fibres of origin of the pectoralis major, forming a thick fibrous membrane, the membrana sterni, which envelopes the sternum. This is more distinct at the lower than at the upper part of the bone. The intraarticular sternocostal ligament, ligamentum sternocostal intraarticular, intraarticular chondro sternal ligament. This ligament is found constantly only between the second costal cartilages and the sternum. The cartilage of the second rib is connected with the sternum by means of an intraarticular ligament, attached by one end to the cartilage of the rib and by the other to the fibrocartilage which unites the manubrium and body of the sternum. This articulation is provided with two synovial membranes. Occasionally, the cartilage of the third rib is connected with the first and second pieces of the body of the sternum by an intraarticular ligament. Still more rarely, similar ligaments are found in the other four joints of the series. In the lower two, the ligament sometimes completely obliterates the cavity so as to convert the articulation into an amphiarthrosis. The costozyphoid ligaments, ligamenta costozyphoidia, chondrozyphoid ligaments. These ligaments connect the anterior and posterior surfaces of the seventh costal cartilage and sometimes those of the sixth to the front and back of the zyphoid process. They vary in length and breadth in different subjects. Those on the back of the joint are less distinct than those on the front. Synovial membranes. There is no synovial membrane between the first costal cartilage and the sternum as this cartilage is directly continuous with the manubrium. There are two in the articulation of the second costal cartilage and generally one in each of the other joints. But those of the sixth and seventh sternocostal joints are sometimes absent. Where an interarticular ligament is present, there are two synovial cavities. After middle life, the articular surfaces lose their polish, become roughened and the synovial membranes apparently disappear. In old age, the cartilages of most of the ribs become continuous with the sternum and the joint cavities are consequently obliterated. Movements. Slight gliding movements are permitted in the sternocostal articulations. Intercondrial articulations. Articulations intercondrales, articulations of the cartilages of the ribs with each other. The contiguous borders of the sixth, seventh and eighth and sometimes those of the ninth and tenth costal cartilages articulate with each other by small, smooth, oblong facets. Each articulation is enclosed in a thin, articular capsule, lined by synovial membrane and strengthened laterally and medially by ligamentous fibres, intercondral ligaments, which pass from one cartilage to the other. Sometimes the fifth costal cartilages, more rarely the ninth and tenth, articulate by their lower borders with the adjoining cartilages by small oval facets. More frequently the connection is by a few ligamentous fibres. Costocondral articulations. The lateral end of each costal cartilage is received into a depression in the sternal end of the rib and the two are held together by the periosteum. Articulation of the manubrium and body of sternum. The manubrium is united to the body of the sternum either by an amphiarthrodial joint, a piece of fibrocartilage connecting the segments, or by a diarthrodial joint in which the articular surface of each bone is clothed with a lamina of cartilage. In the latter case the cartilage covering the body is continued without interruption onto the cartilages of the facets for the second ribs. Rivington found the diarthrodial form of joint in about one-third of the specimens examined by him. Maisonneuve more frequently. It appears to be rare in childhood and is formed in Rivington's opinion from the amphiarthrodial form by absorption. The diarthrodial joint seems to have no tendency to ossify while the amphiarthrodial is more liable to do so and has been found ossified as early as 34 years of age. The two segments are further connected by anterior and posterior intersternal ligaments consisting of longitudinal fibres. Mechanism of the thorax. Each rib possesses its own range and variety of movements, but the movements of all are combined in the respiratory excursions of the thorax. Each rib may be regarded as a lever, the fulcrum of which is situated immediately outside the costotransverse articulation so that when the body of the rib is elevated the neck is depressed and vice versa. From the disproportion in length of the arms of the lever, a slight movement at the vertebral end of the rib is greatly magnified at the anterior extremity. The anterior ends of the ribs lie on a lower plane than the posterior. When therefore the body of the rib is elevated, the anterior extremity is thrust also forward. Again the middle of the body of the rib lies in a plane below that passing through the two extremities so that when the body is elevated, relatively to its ends, it is at the same time carried outward from the median plane of the thorax. Further each rib forms a segment of a curve which is greater than that of the rib immediately above and therefore the elevation of a rib increases the transverse diameter of the thorax in the plane to which it is raised. The modifications of the rib movements at their vertebral ends have already been described on page 302. Further modifications result from the attachments of their anterior extremities and it is convenient therefore to consider separately the movements of the ribs of the three groups vertebrosternal vertebrochondral and vertebral vertebrosternal ribs the first group differs from the others of this group in that its attachment to the sternum is a rigid one this is counterbalanced to some extent by the fact that its head possesses no interarticular ligament and is therefore more movable. The first pair of ribs with the manubrium stern eye move as a single piece the anterior portion being elevated by rotatory movements at the vertebral extremities. In normal quiet respiration the movement of this arc is practically nil. When it does occur the anterior part is raised and carried forward increasing the anterior posterior and transverse diameters of this region of the chest. The movement of the second rib is also slight in normal respiration as its anterior extremity is fixed to the manubrium and prevented therefore from moving upward. The sternocostal articulation however allows the middle of the body of the rib to be drawn up and in this way the transverse thoracic diameter is increased. Elevation of the third, fourth, fifth and sixth ribs raises and thrusts forward their anterior extremities the greater part of the movement being affected by the rotation of the rib neck backward. The thrust of the anterior extremities carries forward and upward the body of the sternum which moves on the joint between it and the manubrium and thus the anterior posterior thoracic diameter is increased. This movement is however soon arrested and the elevating force is then expended in raising the middle part of the body of the rib and diverting its lower border. At the same time the costocondral angle is opened out. By these latter movements a considerable increase in the transverse diameter of the thorax is affected. Vertibrocondral ribs the seventh rib is included with this group as it conforms more closely with their type. While the movements of these ribs assist in enlarging the thorax for respiratory purposes they are also concerned in increasing the upper abdominal space for viscera displaced by the action of the diaphragm. The costal cartilages articulate with one another so that each pushes up that above it. The final thrust being directed to pushing forward and upward the lower end of the body of the sternum. The amount of elevation of the anterior extremities is limited on account of the very slight rotation of the rib neck. Elevation of the shaft is accompanied by an outward and backward movement. The outward movement inverts the anterior end of the rib and opens up the subcostal angle. While the backward movement pulls back the anterior extremity and counteracts the forward thrust due to its elevation. This latter is more noticeable in the lower ribs which are the shortest. The total result is a considerable increase in the transverse and a diminution in the median anterior posterior diameter of the upper part of the abdomen. At the same time however the lateral anterior posterior diameters of the abdomen are increased. Vertible ribs since these ribs have free anterior extremities and only costo-central articulations with no interarticular ligaments they are capable of slight movements in all directions. When the other ribs are elevated these are depressed and fixed to form points of action for the diaphragm. End of section seven recording by Alistair Lord Melbourne Australia 2009 Section 8 of Gray's Anatomy Part 2 This is a LibriVox recording. All LibriVox recordings are in the public domain. For more information or to volunteer please visit LibriVox.org. Recording by Leanne Howlett Anatomy of the Human Body Part 2 by Henry Gray Articulation of vertebral column with pelvis 5H Articulation of the vertebral column with the pelvis the ilio lumbar ligament. The ligaments connecting the fifth lumbar vertebra with the sacrum are similar to those which join the movable segments of the vertebral column with each other. Vs. 1. The continuation downward of the anterior and posterior longitudinal ligaments. 2. The intervertebral fibrocartilage connecting the body of the fifth lumbar to that of the first sacral vertebra and forming an amphiarthrodial joint. 3. Ligamenta Flava uniting the lamini of the fifth lumbar vertebra with those of the first sacral. 4. Capsules connecting the articular processes and forming a double arthrodia. 5. Enter and supraspinal ligaments. On either side an additional ligament, the ilio lumbar connects the pelvis with the vertebral column. The ilio lumbar ligament, ligamentum ilio lumbale. The ilio lumbar ligament is attached above to the lower and front part of the transverse process of the fifth lumbar vertebra. It radiates as it passes lateralward and is attached by two main bands to the pelvis. The lower bands run to the base of the sacrum, blending with the anterior sacroiliac ligament. The upper is attached to the crest of the ilium immediately in front of the sacroiliac articulation and is continuous above with the lumbodorsal fascia. In front it is in relation with the psoas major. Behind with the muscles occupying the vertebral groove. Above with the quadratus lumborum. 5. Eye articulations of the pelvis. The ligaments connecting the bones of the pelvis with each other may be divided into four groups. 1. Those connecting the sacrum and ilium. 2. Those passing between the sacrum and ischium. 3. Those uniting the sacrum and cossacks. 4. Those between the two pubic bones. 1. Sacroiliac articulation. Articulatio sacroiliaca. The sacroiliac articulation is an amphiarthrodial joint formed between the auricular surfaces of the sacrum and the ilium. The articular surface of each bone is covered with a thin plate of cartilage thicker on the sacrum than on the ilium. These cartilaginous plates are in close contact with each other and to a certain extent are united together by irregular patches of softer fibrocartilage and at their upper and posterior part by fine enterosius fibers. In a considerable part of their extent, especially in advanced life, they are separated by a space containing a synovia-like fluid and hence the joint presents the characteristics of a diarthrosis. The ligaments of the joint are the anterior sacroiliac, the posterior sacroiliac, the enterosius, the anterior sacroiliac ligament, ligamentum sacroiliacum anteriorus. The anterior sacroiliac ligament consists of numerous thin bands which connect the anterior surface of the lateral part of the sacrum to the margin of the auricular surface of the ilium and to the pre-auricular sulcus. The posterior sacroiliac ligament, ligamentum sacroiliacum posteriorus. The posterior sacroiliac ligament is situated in a deep depression between the sacrum and ilium behind. It is strong and forms the chief bond of union between the bones. It consists of numerous vesiculi which pass between the bones in various directions. The upper part, short posterior sacroiliac ligament, is nearly horizontal in direction and pass from the first and second transverse tubercles on the back of the sacrum to the tuberosity of the ilium. The lower part, long posterior sacroiliac ligament, is oblique in direction. It is attached by one extremity to the third transverse tubercle of the back of the sacrum and by the other to the posterior superior spine of the ilium. The enterosius sacroiliac ligament, ligamentum sacroiliacum enterosium. This ligament lies deep to the posterior ligament and consists of a series of short, strong fibers connecting the tuberosities of the sacrum and ilium. Two, ligaments connecting the sacrum and ischium. The sacrotuberous, the sacrospinus. The sacrotuberous ligament, ligamentum sacrotuberosum, great or posterior sacrosciatic ligament. The sacrotuberous ligament is situated at the lower and back part of the pelvis. It is flat and triangular in form, narrower in the middle than at the ends, attached by its broad base to the posterior inferior spine of the ilium, to the fourth and fifth transverse tubercles of the sacrum, and to the lower part of the lateral margin of that bone and the cossacks. Passing obliquely downward, forward, and lateral word, it becomes narrow and thick, but at its insertion into the inner margin of the tuberosity of the ischium, it increases in breadth and is prolonged forward along the inner margin of the ramus as the falciform process. The freconcave edge of which gives attachment to the obturator fascia. One of its surfaces is turned toward the perineum, the other toward the obturator internus. The lower border of the ligament is directly continuous with the tendon of origin of the long head of the biceps femoris, and by many is believed to be the proximal end of this tendon, cut off by the projection of the tuberosity of the ischium. Relations. The posterior surface of this ligament gives origin, by its whole extent, to the gluteus maximus. Its anterior surface is in part united to the sacrospinus ligament. Its upper border forms above the posterior boundary of the greater sciatic foramen, and below the posterior boundary of the lesser sciatic foramen. Its lower border forms part of the boundary of the perineum. It is pierced by the coxigial nerve and the coxigial branch of the inferior gluteal artery. The sacrospinus ligament. Ligamentum sacrospinosum, small or anterior sacrosciatic ligament. The sacrospinus ligament is thin and triangular in form. It is attached by its apex to the spine of the ischium, and medially by its broad base to the lateral margins of the sacrum and coccyx in front of the sacrotuberous ligament with which its fibers are intermingled. Relations. It is in relation anteriorly with a coxigius muscle to which it is closely connected. Posteriorly, it is covered by the sacrotuberous ligament and crossed by the internal pudendal vessels and nerve. Its upper border forms the lower boundary of the greater sciatic foramen. Its lower border part of the margin of the lesser sciatic foramen. These two ligaments convert the sciatic notches into foramina. The greater sciatic foramen is bounded in front and above by the posterior border of the hip bone, behind by the sacrotuberous ligament and below by the sacrospinus ligament. It is partially filled up in the recent state by the pyreformus which leaves the pelvis through it. Above this muscle, the superior gluteal vessels and nerve emerge from the pelvis, and below it the inferior gluteal vessels and nerve, the internal pudendal vessels and nerve, the sciatic and posterior femoral cutaneous nerves, and the nerves to the obturator internus and quadratus femoris make their exit from the pelvis. The lesser sciatic foramen is bounded in front by the tuberosity of the ischium, above by the spine of the ischium and sacrospinus ligament, behind by the sacrotuberous ligament. It transmits the tendon of the obturator internus, its nerve, and the internal pudendal vessels and nerve. 3. Sacrocoxygeal synthesis, synthesis sacrocoxygia, articulation of the sacrum and cossacks. This articulation is an amphiarthrodial joint, formed between the oval surface at the apex of the sacrum and the base of the cossacks. It is homogalous with the joints between the bodies of the vertebrae and is connected by similar ligaments. They are the anterior sacrocoxygeal, the posterior sacrocoxygeal, the lateral sacrocoxygeal, the interposed fibrocartilage, the interarticular. 4. The anterior sacrocoxygeal ligament, ligamentum sacrocoxygium anteriorus. This consists of a few irregular fibers, which descend from the anterior surface of the sacrum to the front of the cossacks, blending with the periosteum. The posterior sacrocoxygeal ligament, ligamentum sacrocoxygium posteriorus. This is a flat band, which arises from the margin of the lower orifice of the sacral canal and descends to be inserted into the posterior surface of the cossacks. This ligament completes the lower and back part of the sacral canal and is divisible into a short, deep portion and a longer superficial part. It is in relation behind with the gluteus maximus. The lateral sacrocoxygeal ligament, ligamentum sacrocoxygium lateral intertransverse ligament. The lateral sacrocoxygeal ligament exists on either side and connects the transverse process of the cossacks to the lower lateral angle of the sacrum. It completes the foreamen for the fifth sacral nerve. A disc of fibrocartilage is interposed between the contiguous surfaces of the sacrum and coccyx. It differs from those between the bodies of the vertebrae in that it is thinner and its central part is firmer in texture. It is somewhat thicker in front and behind than at the sides. Occasionally, the coccyx is freely movable on the sacrum, most notably during pregnancy. In such cases, the synovial membrane is present. The intraarticular ligaments are thin bands which unite the cornea of the two bones. The different segments of the coccyx are connected by the extension downmer of the anterior and posterior sacrocoxygeal ligaments, thin annular discs of fibrocartilage being interposed between the segments. In the adult male, all the pieces become ossified together at a comparatively early period. But in the female, this does not commonly occur until a later period of life. At more advanced age, the joint between the sacrum and coccyx is obliterated. Movements. The movements which take place between the sacrum and coccyx and between the different pieces of the latter bone are forward and backward. They are very limited. Their extent increases during pregnancy. 4. The pubic symphysis. Symphysis oseum pubis. Articulation of the pubic bones. The articulation between the pubic bones is an amphoarthrodial joint formed between the two oval articular surfaces of the bones. The ligaments of this articulation are the anterior pubic, the posterior pubic, the superior pubic, the arcuate pubic, the interpubic fibrocartilaginous lamina, the anterior pubic ligament. The anterior pubic ligament consists of several superimposed layers which pass across the front of the articulation. The superficial fibres pass obliquely from one bone to the other, decasating and forming an interlacement with the fibres of the aponeuroses of the obloquy externi and the medial tendons of origin of the recti abdominis. The deep fibres pass transversely across the symphysis and are blended with the fibrocartilaginous lamina. The posterior pubic ligament. The posterior pubic ligament consists of a few thin scattered fibres which unite the two pubic bones posteriorly. The superior pubic ligament. Ligamentum pubicum superius. The superior pubic ligament connects together the two pubic bones superiorly extending laterally as far as the pubic tubercles. The arcuate pubic ligament. Ligamentum arcuatum pubis inferior pubic or sub pubic ligament. The arcuate pubic ligament is a thick triangular arch of ligamentous fibres connecting together the two pubic bones below and forming the upper boundary of the pubic arch. Above, it is blended with the inter pubic fibrocartilaginous lamina. Laterally, it is attached to the inferior rami of the pubic bones. Below, it is free and is separated from the fascia of the urogenital diaphragm by an opening through which the deep dorsal vein of the penis passes into the pelvis. The inter pubic fibrocartilaginous lamina. Lamina, fibrocartilagina, intrapubica, intrapubic disc. The intrapubic fibrocartilaginous lamina connects the opposed surfaces of the pubic bones. Each of these surfaces is covered by a thin layer of high-aligned cartilage firmly joined to the bone by a series of nipple-like processes which accurately fit into corresponding depressions on the oseous surfaces. These opposed cartilaginous surfaces are connected together by an intermediate lamina of fibrocartilage which varies in thickness in different subjects. It often contains a cavity in its interior, probably formed by the softening and absorption of the fibrocartilage since it rarely appears before the tenth year of life and is not lined by synovial membrane. This cavity is larger in the female than in the male, but it is very doubtful whether it enlarges as was formerly supposed during pregnancy. It is most frequently limited to the upper and back part of the joint. It occasionally reaches to the front and may extend the entire length of the cartilage. It may be easily demonstrated when present by making a coronal section of the symphysis pubis near its posterior surface. Mechanism of the pelvis. The pelvic girdle supports and protects the contained viscera and affords surfaces for the attachments of the trunk and lower limb muscles. Its most important mechanical function, however, is to transmit the weight of the trunk and upper limbs to the lower extremities. It may be divided into two arches by a vertical plane passing through the acetabular cavities. The posterior of these arches is the one chiefly concerned in the function of transmitting the weight. Its essential parts are the upper three sacral vertebrae and two strong pillars of bone running from the sacroiliac articulations to the acetabular cavities. For the reception and diffusion of the weight, each acetabular cavity is strengthened by two additional bars running toward the pubis and ischium. In order to lessen concussion and rapid changes of distribution of the weight, joints, sacroiliac articulations are interposed between the sacrum and the iliac bones. An accessory joint, pubis symphysis, exists in the middle of the anterior arch. The sacrum forms the summit of the posterior arch. The weight transmitted falls on it at the lumbosacral articulation and theoretically has a component in each of two directions. One component of the force is expended in driving the sacrum downward and backward between the iliac bones, while the other thrusts the upper end of the sacrum downward and forward toward the pelvic cavity. The movements of the sacrum are regulated by its form. Viewed as a whole, it presents the shape of a wedge with its base upward and forward. The first component of the force is therefore acting against the resistance of the wedge and its tendency to separate the iliac bones is resisted by the sacroiliac and iliolumbar ligaments and by the ligaments of the pubic synthesis. If a series of coronal sections of the sacroiliac joints be made, it will be found possible to divide the articular portion of the sacrum into three segments, anterior, middle, and posterior. In the anterior segment, which involves the first sacral vertebra, the articular surfaces show slight sinuosities and are almost parallel to one another. The distance between their dorsal margins is, however, slightly greater than that between their ventral margins. This segment therefore presents a slight wedge shape with the truncated apex downward. The middle segment is a narrow band across the centers of the articulations. Its dorsal width is distinctly greater than its ventral, so that the segment is more definitely wedge-shaped, the truncated apex being again directed downward. Each articular surface presents in the center a marked concavity from above downward and into this a corresponding convexity of the iliac articular surface fits, forming an interlocking mechanism. In the posterior segment, the ventral width is greater than the dorsal, so that the wedge form is the reverse of those of the other segments, i.e., the truncated apex is directed upward. The articular surfaces are only slightly concave. Dislocation downward and forward of the sacrum by the second component of the fore supplied to it is prevented therefore by the middle segment, which interposes the resistance of its wedge shape and that of the interlocking mechanism on its surfaces. A rotary movement, however, is produced by which the anterior segment is tilted downward in the posterior upward. The axis of this rotation passes through the dorsal part of the middle segment. The movement of the anterior segment is slightly limited by its wedge form, but chiefly by the posterior and interosseous sacroiliac ligaments. That of the posterior segment is checked to a slight extent by its wedge form, but the chief limiting factors are the sacrotuberous and sacrospinous ligaments. In all these movements, the effect of the sacroiliac and iliolumbar ligaments and the ligaments of the symphysis pubis in resisting the separation of the iliac bones must be recognized. During pregnancy, the pelvic joints and ligaments are relaxed and capable therefore of more extensive movements. When the fetus is being expelled, the force is applied to the front of the sacrum. Upward dislocation is again prevented by the interlocking mechanism of the middle segment. As the fetal head passes the anterior segment, the ladder is carried upward, enlarging the anterior posterior diameter of the pelvic inlet. When the head reaches the posterior segment, this also is pressed upward against the resistance of its wedge, the movement only being possible by the laxity of the joints and the stretching of the sacrotuberous and sacrospinous ligaments. End of section 8, recording by Leanne Howlett.