Skull Osteology

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Two parts of the skull

Neurocranium and Viscerocranium

Neurocranium

forms a protective vault containing the brain

Viscerocranium

forms the skeleton of the face

Foramen

an aperture or perforation through a bone or a membranous structure

Hiatus

an aperture, gap, or fissure

Iter

A passage leading from one anatomical space to another

Paries

A wall, as of the chest, abdomen, or any hollow organ

Sinus

a general term for such spaces as the dilated channels for venous blood inside teh cranial cavity or teh air cavities in cranial bones which communicate with the nasal cavities

Somatic

relating to the soma or trunk or the wall of the body cavity; parietal

Squama

A thin plate of bone

Viscus

An organ of teh digestive, respiratory, urogenital, or endocrine systems as well as the spleen, the heart and the blood vessels; hollow and multilayered walled organs

Squama

flat surface forming the forehead

Frontal eminences

rounded elevations about 3 cm above each supraorbital margin

Supraorbital margins

superior borders of each orbit

Superciliary arches

prominent elevation above each supraorbital margin

Glabella

flat area of bone between superciliary arches

Zygomatic process

articulates with the zygomatic bone

Temporal lines

bilateral ridge arching superiorly and posteriorly from zygomatic process. Origin of m. temporalis. Demarcates the superior limit of the temporal fossa.

Nasion

midpoint of frontonasal suture

Sagittal sulcus

linear midline depression (internal); lodges parts of superior sagittal sinus (a large vein formed from periosteum and dural membranes)

Frontal crest

attachment for the falx cerebri

Orbital plates

forms roof of orbit

Lacrimal fossa

anterior and lateral depression of roof of orbit which accommodates the lacrimal gland

Ethmoidal notch

midline gap between orbital plates (only evident if ethmoid bone is removed)

Frontal air sinuses

cavities between bony plates of superciliary arches and cranial cavity

Foramen caecum

found at midpoint of frontoethmoidal articulation

Supraorbital foramen or notch

in medial 1/3 of supraorbital border and transmits supraorbital nerve, artery, and vein (NVB); occasionally multiple

Parietal eminence

smooth elevation near center of each bone

Temporal lines

continuous with temporal lines of frontal bone

Bregma

point of intersection of coronal (fronto-parietal) and sagittal sutures (site of anterior, or bregmatic, fontanelle in the newborn)

Lambda

point of intersection of lambdoidal (occipito-parietal) and sagittal sutures (site of posterior fontanelle in infants)

Parietal Foramina

Posteriorly, on either side of the sagittal suture; when present, it tranmits veins from the scalp to superior sagittal sinus (emissary veins)

External occipital protuberance

prominence midway between lambda and foramen magnum (=inion)

Superior nuchal line

ridges extending laterally from external occipital protuberance

Median nuchal line

crest descending from external occipital protuberance to foramen magnum;

Inferior nuchal line

ridges extending laterally from midpoint (at median nuchal line)

Internal occipital protruberance

(internal) midway between lambda and foramen magnum

Sagittal sulcus

groove extending superiorly from internal occipital protuberance

Internal occipital crest

ridge extending inferiorly from internal occipital protuberance

Grooves for transverse sinuses

extend laterally from internal occipital protuberance

Depression for confluence of sinuses (Torcular of Herophili)

at intersection of superior sagittal, transverse, occipital, and straight venous sinuses; may be on the right or left side of the midline

Condyles

articulate with atlas (the first cervical, or neck, vertebrae)

Condyloid fossae

posterior to each condyle; accomodate posterior margin of superior facet of atlas when head is bent backward

Pharyngeal tubercle

Anterior to foramen magnum, this is the attachment site for fibrous raphe of pharynx in the midline

Grooves for the inferior petrosal sinuses

(internal) along the anterior lateral margins

Condyloid Canal

Posterior to each condyle in condyloid fossa

Hypoglossal canal (anterior condyloid)

at anterior base of each condyle, this canal transmits hypoglossal nerve (XII) and meningeal branch of ascending pharyngeal artery

Jugular notch

on the anterior-lateral margin of the occipital bone - lateral to each condyle

Jugular notch becomes:

posterior margin of the jugular foramen

Jugular foramen

The jugular notch of the occipital bone, together with the jugular fossa of the temporal bone form a large foramen when these bones are articulated

Jugular foramen transmits:

CN XI (accessory), CN X (vagus) and the CN IX (glossopharyngeal).

Sinuses that drain into the jugular bulb:

INferior petrosal venous sinus passes over its lateral margin; the inferior petrosal venous sinus and the sigmoid sinus merge to form the internal jugular vein

Jugular bulb

a dilation at the top of the internal jugular vein; occupies the jugular fossa of the temporal bone

Foramen magnum

transmits spinal cord and meninges; vertebral arteries; vertebral venous plexus and CV XI

Zygomatic Process

articulates with zygomatic bone to form the zygomatic arch

Articular tubercle

eminence of anterior root of zygomatic process;

Temporal lines

continuous with those of frontal and parietal bones

Mandibular (glenoid) fossa

bounded anteriorly by the articular tubercle;

Petrotympanic fissure

splits the mandibular (glenoid) fossa

Suprameatal triangle

posterior-superior to external auditory meatus; an instrument may be pushed through the bone here into the tympanic antrum or middle ear chamber

External acoustic (auditory) meatus

bony part of external ear; extends about 2.5 cm anterior-lateral to tympanic membrane

Styloid process

bony projection extending antero-inferiorly from inferior surface of tympanic portion of temporal

Mastoid process

large downward projection containing air cells, posterior to tympanic part of temporal bone

Mastoid (digastric) notch / Digastric Groove

deep groove on medial aspect of mastoid prcoess

Occipital groove

just medial to mastoid notch; impression made by a occipital artery

Arcuate eminence

on antero-lateral surface; indicates position of superior semi-circular canal

Trigeminal impression

anterior surface near apex (above internal aperture of carotid canal). Lodges semilunar gasserian ganglion of CN V, trigeminal

Jugular fossa

the inferior surface of this fossa forms the anterior part of the jugular foramen; lodges bulb of the internal jugular vein in this deep fossa

Aquaeductus cochleae

fossa in the triangular depression posterior to external orifice of carotid canal; inferior to internal auditory meatus; contains a dural communication between perilymphatic and subarachnoid spaces (fluid-filled)

Aquaeductus vestibulae

posterior lateral to internal auditory meatus; transmits ductus endolympathicus (fluid filled) of the inner ear

Carotid canal

inferior petrous part, transmits internal carotid artery and carotid plexus

External auditory meatus

facial canal-bony canal transmitting portions of the facial N through the petrous pyramid to the stylomastoid foramen

Foramen lacerum

deficiency in floor of middle cranial fossa, anterior medial to internal orifice of teh carotid canal. In life, inferior part is filled with fibrocartilage over which courses the internal carotid artery and trhough which passes the nerve of the pterygoid canal (Vidian N) and a meningeal branch of the ascending pharyngeal artery

Hiatus of the facial nerve

anterior surface of petrous portion; transmits greater petrosal nerve (branch of CN VII)

internal acoustic meatus

located on the posterior surface of the petrous portion; transmits the facial nerve (CN VII) and the vestibulocochlear nerve (CN VIII) and the internal auditory branch of the basilar artery

Nasion

frontal and nasal bones meet here

Frontal crest

a projection of the dural membrane between the left and right cerebral hemispheres

Ethmoid notch

accommodates cribiform plate of ethmoid bone

Superior nuchal line

Origin of mm occiptalis, trapezius, sternocleidomastoid and splenius capitis

Median nuchal line

Origin of attachment of ligamentum nuchae

Inferior nuchal line

Insertion of mm. rectus capitis posterior major and minor

Condyloid canal

This canal transmits emissary vein

Internal jugular vein

forms from the merger of the inferior petrosal sinus and the sigmoid sinus

Articular tubercle

forms anterior boundary of mandibular fossa and attachment of temporomandibular ligament

Mandibular fossa

fossa is bound posteriorly by the tympanic part of the temporal bone

Mandibular fossa

anterior part receives the mandibular condyle; and the posterior is non-articular and lodges a small portion of the parotid gland

Styloid process

Origin for mm. Stylohyoid, styloglossus, and stylopharyngeus; and attachment for stlyohyold and sytlomandibular ligaments;

Mastoid process

attachment for m. stenocleidomastoid, splenius capitis, and longissimus capitis

Mastoid (diagastric) notch

attachment for m. digastric (posterior belly)

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