Advertisement Upgrade to remove ads


Divided into 2 main sets of bones: 8 cranial and 14 facial.

Calvaria (Skullcap)

Consists of the frontal, right & left parietal, and occipital bones


Consists of the right & left temporal, sphenoid, and ethmoid bones

Frontal Bone

Contributes to the formation of the forehead and the superior part of each orbit

2 main parts: Squamous and Orbital portions

Squamous Portion (of frontal bone)

Also known as the vertical portion

Forms the forehead

Orbital Portion

Also known as the Horizontal portion

Forms the superior part of the orbit


The smooth, raised prominence between the eyebrows just above the bridge of the nose

Supraorbital Groove (SOG)

The slight depression above each eyebrow.

At the highest level of the orbital plate or at the highest level of the facial bone mass

Supraorbital Margin (SOM)

The superior rim of each orbit

Supraorbital Notch

A small hole or opening within the supraorbital margin slightly medial to its midpoint

Frontal Tuberosity

A large rounded prominence above each supraorbital groove

Ethmoidal Notch

Separates the orbital plates

Part of the frontal bone

Orbital Plate

Forms the superior part of each orbit

Parietal Bones

Makes up the lateral walls of the cranium and part of the roof

Parietal Tubercles (Eminences)

The widest portion of the entire skull

Occipital Bone

Makes up the inferoposterior portion of the calvaria

External Occipital Protuberance

Also known as the Inion

The prominent bump or protuberance at the inferoposterior portion of the skull

Foramen Magnum

Means "great hole"

Large opening at the base of the occipital bone through which the spinal cord passes as it leave the brain

Atlantooccipital Joint

Articulation between the skull and the cervical spine

Condylar Portions (Occipital Condyles)

Oval processes with convex surfaces on each side of the foramen magnum

Temporal Bones

Houses the delicate organs for hearing and balance

Zygomatic Process

Extending anteriorly from the squamous portion of the temporal bone

Zygomatic Arch

Formed by the zygomatic process of the temporal and zygomatic bones

Styloid Process

Slender bony projection inferior to the mandible and anterior to the EAM

Squamous Portion (of Temporal bone)

Thin upper portion that forms part of the wall of the skull

Most vulnerable portion of the entire skull to fracture

Mastoid Portion

Posterior to the EAM

Houses the mastoid air cells

Petrous Portion

Also known as the petrous pyramid or pars petrosa

Houses the organs of hearing and equilibrium

The most dense portion of the temporal bone

Petrous Ridge

The upper border or ridge of the petrous pyramids

Corresponds to the level of the TEA (top of the ear attachment)

Internal Acoustic Meatus

Opening or orifice which serves to transmit the nerves of hearing and equilibrium

Sphenoid Bone

Single, centrally located bone which serves as an anchor for all 8 cranial bones

Sella Turcica

The central depression on the body of the sphenoid bone

Partially surrounds and protects the pituitary gland (hypophysis cerebri)

Dorsum Sellae

Posterior to the sella turcica


A shallow depression that begins on the posteroinferior aspect of the dorsum sellae and extends posteriorly to the foramen magnum

Lesser Wings

Small, triangular pair of wings of the sphenoid bone

Greater Wings

Pair of wings that extends laterally from the sides of the sphenoid body

Superior Orbital Fissures

Irregularly shaped openings that provide additional communication with the orbits for numerous cranial nerves and blood vessels

Cribriform Plate

Smaller upper horizontal portion of the ethmoid bone

Crista Galli

Also known as the Rooster's Comb

Projects superiorly from the cribriform plate

Perpendicular Plate

Downward projection of the ethmoid bone which helps form the bony nasal septum

Lateral labyrinths (masses)

Contains the ethmoid air cells of sinuses and help to form the medial walls of the orbits and the lateral walls of the nasal cavity

Superior & Middle Nasal Conchae

Also known as turbinates

Thin scroll-shaped projections of bone extending medially and downward from the wall of each labyrinth


Articulations or joints of the cranium

Coronal Suture

Separates the frontal bone from the 2 parietal bones

Sagittal Suture

Separates the 2 parietal bones

Lambdoidal Suture

Separates the 2 parietal bones from the occipital bone

Squamosal Suture

Formed by the inferior junctions of the 2 parietal bones with their respective temporal bones


Anterior end of the sagittal suture


Posterior end of the sagittal suture


Points at the junction of the parietals, temporals and the greater wings of the sphenoid


Points posterior to the ear where the squamosal and lambdoidal sutures meet


Areas of the infant cranium where the sutures meet

Anterior/Posterior Fontanels

Soft spots in an infant corresponding to the bregma and lambda of an adult cranium

Anterior fontanel is the largest

Sphenoid Fontanels

Corresponds to the Pterions in an adult cranium

Mastoid Fontanels

Corresponds to the Asterions in an adult cranium

Wormian (Sutural) Bones

Smal, irregular bones often found in the lambdoidal suture


The small liplike structure located anterior to the EAM that acts as a partial shield to the ear opening

External Acoustic Meatus (EAM)

The opening or canal of the external ear

Tympanic Membrane

Part of the middle ear that serves as a partition between the external and middle ears

Epitympanic Recess (Attic)

The area above the level of the EAM and eardrum

Eustachian Tube

The passageway between the middle ear and the nasopharynx.

Serves to equalize the pressure within the middle ear to the outside atmospheric air pressure through the nasopharynx

Tegmen Tympani

The thin plate of bone that forms the roof of the antrum, aditus, and attic area of the tympanic cavity

Internal Ear

Contains the essential sensory apparatus of both hearing and equilibrium

Lies within the densest portion of the petrous pyramid

Endolymphatic Duct

A blind pouch or closed duct contained in a small canal-like, bony structure

Semicircular Canals

Located posterior to the other inner ear structures

Relates to the sense of direction and equilibrium


The most anterior part of the osseous lanyrinth

Relates to the sense of hearing


Shape of the average head

Width is between 75% and 80% of the length

Petrous pyramids form an angle of 47 degrees


Short, broad head

Width is 80% or greater than the length

Petrous pyramids form an angle greater than 47 degrees


Long, narrow head

Width is less than 75% of the length

Petrous pyramids form an angel less than 47 degrees

Midsagittal Plane (MSP)

Divides the body into equal left and right halves

Interpupillary Line

A line that connects the pupils or the outer canthi of the patient's eyes

Superciliary Arch

Ridge or arch of bone that extends across the forehead directly above each eye

Supraorbital Groove (SOG)

A slight groove or depression above the superciliary arch


Located at the junction of the 2 nasal bones and the frontal bone


The midline point at the junction of the upper lip and the nasal septum

Gonion (Angle)

Refers to the lower posterior angle on each side of the jaw or mandible

Mentum (Chin)

A flat triangular area

Mental Point

The midpoint of the mentum

Auricle or Pinna

The large flap of ear made of cartilage

Inner Canthus

Where the eyelids meet near the nose

Outer Canthus

Lateral junction of the eyelids

Infraorbital Margin (IOM)

The inferior rim of the bony orbit of the eye

Auricular Point

The center point of the EAM

Glabellomeatal Line (GML)

Line between the glabella and the EAM

Orbitomeatal Line (OML)

Line between the outer canthus and the EAM

Infraorbitomeatal Line (IOML)

Line connecting the infraorbital margin to the EAM

Older terms: Reid's or Anthropologic base line

7-8 degree difference between the OML and IOML

Acanthiomeatal Line (AML)

Line between the acanthion and the EAM

Mentomeatal Line (MML)

Line between the mental point and the EAM

Lips-meatal Line (LML)

A line between the junction of the lips to the EAM

Glabelloalveolar Line (GAL)

Connects the glabella to a point at the anterior aspect of the alveolar process of the maxilla

Linear Fractures

Fractures of the skull that may appear as jagged or irregular lucent lines that lie at right angles to the axis of the bone

Depressed Fractures

Also known as Ping-Pong Fractures

A fragment of bone that is separated and depressed into the cranial cavity can occur

Basal Skull Fractures

Fractures through the dense inner structures of the temporal bone

Multiple Myeloma

Consists of one or more bone tumors that originate in the bone marrow

Pituitary adenomas

Tumors of the pituitary gland

Paget's Disease

Also known as Osteitis Deformans

A disease of unknown origin that begins as a stage of bony destruction followed by bony repair


Acute mastoiditis is a bacterial infection of the mastoid process that can destroy the inner part of the mastoid process

Acoustic Neuroma

Benign tumor of the auditory nerve sheath that originates in the internal auditory canal


Benign cystlike mass or tumor, which is common in the middle ear or mastoid region secondary to trauma to this region, destroys bone


Growth arising from mucous membrane and projects into a cavity may cause chronic sinusitis


Hereditary disease which involves excessive spongy bone formation of the middle and inner ear

Most common cause of hearing loss in adults

Please allow access to your computer’s microphone to use Voice Recording.

Having trouble? Click here for help.

We can’t access your microphone!



Reload the page to try again!


Press Cmd-0 to reset your zoom

Press Ctrl-0 to reset your zoom


Please upgrade Flash or install Chrome
to use Voice Recording.

For more help, see our troubleshooting page.

Your microphone is muted

For help fixing this issue, see this FAQ.

Star this term

You can study starred terms together

NEW! Voice Recording