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100 terms

Ch 12: Skull & Cranial Bones

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Skull
Divided into 2 main sets of bones: 8 cranial and 14 facial.
Calvaria (Skullcap)
Consists of the frontal, right & left parietal, and occipital bones
Floor
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
Glabella
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
Clivus
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
Sutures
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
Bregma
Anterior end of the sagittal suture
Lambda
Posterior end of the sagittal suture
Pterions
Points at the junction of the parietals, temporals and the greater wings of the sphenoid
Asterions
Points posterior to the ear where the squamosal and lambdoidal sutures meet
Fontanels
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
Tragus
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
Cochlea
The most anterior part of the osseous lanyrinth

Relates to the sense of hearing
Mesocephalic
Shape of the average head

Width is between 75% and 80% of the length

Petrous pyramids form an angle of 47 degrees
Brachycephalic
Short, broad head

Width is 80% or greater than the length

Petrous pyramids form an angle greater than 47 degrees
Dolichocephalic
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
Nasion
Located at the junction of the 2 nasal bones and the frontal bone
Acanthion
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
Mastoiditis
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
Cholesteatoma
Benign cystlike mass or tumor, which is common in the middle ear or mastoid region secondary to trauma to this region, destroys bone
Polyp
Growth arising from mucous membrane and projects into a cavity may cause chronic sinusitis
Otosclerosis
Hereditary disease which involves excessive spongy bone formation of the middle and inner ear

Most common cause of hearing loss in adults