Squamous part of occipital bone

Squamous part of occipital bone
Human skull seen from above (parietal bones removed). Squamous part is shown in red.
Occipital bone at birth, seen from below. (Squamous part is top half, portion above foramen magnum, shown in yellow.)
Details
Identifiers
Latin	squama occipitalis
TA	A02.1.04.010
FMA	52860
*Anatomical terms of bone* [edit on Wikidata]

The squamous part of occipital bone, is situated above and behind the foramen magnum, and is curved from above downward and from side to side.

External surface

The external surface is convex and presents midway between the summit of the bone and the foramen magnum a prominence, the external occipital protuberance and inion.

Extending lateralward from this on either side are two curved lines, one a little above the other. The upper, often faintly marked, is named the highest nuchal line, and to it the epicranial aponeurosis is attached.

The lower is termed the superior nuchal line. That area of the squamous part, which lies above the highest nuchal lines is named the occipital plane and is covered by the occipitalis muscle. That below, termed the nuchal plane, is rough and irregular for the attachment of several muscles.

From the external occipital protuberance, an often faintly marked ridge or crest, the median nuchal line, descends to the foramen magnum and affords attachment to the nuchal ligament. Running from the middle of this line across either half of the nuchal plane is the inferior nuchal line.

Several muscles are attached to the outer surface of the squamous part, thus the superior nuchal line gives origin to the occipitalis and trapexius muscles, and insertion to the sternocleidomastoid and splenius capitis muscles. Into the surface between the superior and inferior nuchal lines the semispinalis capitis and the obliquus capitis superior are inserted, while the inferior nuchal line and the area below it receive the insertions of the rectus capitis posterior major and minor.

The posterior atlantooccipital membrane is attached around the postero-lateral part of the foramen magnum, just outside the margin of the foramen.

Internal surface

The internal surface is deeply concave and divided into four fossae by a cruciate eminence.

The upper two fossae are triangular and lodge the occipital lobes of the cerebrum; the lower two are quadrilateral and accommodate the hemispheres of the cerebellum.

At the point of intersection of the four divisions of the cruciform eminence is the internal occipital protuberance.

From this protuberance the upper division of the cruciform eminence runs to the superior angle of the bone, and on one side of it (generally the right) is a deep groove, the sagittal sulcus, which lodges the hinder part of the superior sagittal sinus. To the margins of this sulcus the falx cerebri is attached.

The lower division of the cruciform eminence is prominent and is named the internal occipital crest; it bifurcates near the foramen magnum and gives attachment to the falx cerebelli. In the attached margin of this falx is the occipital sinus, which is sometimes duplicated.

In the upper part of the internal occipital crest, a small depression is sometimes distinguishable; it is termed the vermian fossa since it is occupied by part of the vermis of the cerebellum. Transverse grooves, one on either side, extend from the internal occipital protuberance to the lateral angles of the bone; those grooves accommodate the transverse sinuses, and their prominent margins give attachment to the tentorium cerebelli.

The groove on the right side is usually larger than that on the left and is continuous with that for the superior sagittal sinus.

Exceptions to this condition are, however, not infrequent: the left may be larger than the right or the two may be almost equal in size.

The angle of union of the superior sagittal and transverse sinuses is named the confluence of the sinuses, and its position is indicated by a depression situated on one or other side of the protuberance.

Additional images

Human skull seen from below. Squamous part is shown red.
Occipital bone, inner surface. Squamous part is shown red.
Occipital bone, inner surface. (Squamous part is top half, portion above foramen magnum.)

Wikimedia Commons has media related to Squamous part of occipital bone.

References

This article incorporates text in the public domain from the 20th edition of Gray's Anatomy (1918)

The neurocranium of the skull

Occipital

Squamous part	external Inion/External occipital protuberance External occipital crest Nuchal lines planes Occipital Nuchal internal Cruciform eminence Internal occipital protuberance Sagittal sulcus Internal occipital crest Groove for transverse sinus

Lateral parts	Condyle Condyloid fossa Condylar canal Hypoglossal canal jugular Jugular process Jugular tubercle

Basilar part	Pharyngeal tubercle Clivus

Other	Foramen magnum Basion Opisthion

Parietal

Frontal

Squamous part	Frontal suture Frontal eminence external Superciliary arches Glabella foramina Supraorbital Cecum Zygomatic process internal Sagittal sulcus Frontal crest

Orbital part	Ethmoidal notch Fossa for lacrimal gland Trochlear fovea Frontal sinus Frontonasal duct

Temporal

Squamous part	Articular tubercle Suprameatal triangle Mandibular fossa Petrotympanic fissure Zygomatic process

Mastoid part	Mastoid foramen Mastoid process (Mastoid cells) Mastoid notch Occipital groove Sigmoid sulcus Mastoid antrum (Aditus)

Petrous part	Carotid canal Facial canal Hiatus Internal auditory meatus Cochlear aqueduct Stylomastoid foramen fossae Subarcuate fossa Jugular fossa canaliculi Inferior tympanic Mastoid Styloid process Petrosquamous suture (note: ossicles in petrous part, but not part of temporal bone)

Tympanic part	Suprameatal spine

Sphenoid

Surfaces	Superior surface: Sella turcica Dorsum sellae Tuberculum sellae Hypophysial fossa Posterior clinoid processes Ethmoidal spine Chiasmatic groove Middle clinoid process Petrosal process Clivus Lateral surface: Carotid groove Sphenoidal lingula Anterior surface: Sphenoidal sinuses

Great wings	foramina Rotundum Ovale Vesalii Spinosum Spine Infratemporal crest Sulcus of auditory tube

Small wings	Superior orbital fissure Anterior clinoid process Optic canal

Pterygoid processes	fossae Pterygoid Scaphoid pterygoid plates Lateral Medial Pterygoid canal Hamulus

Other	Body Sphenoidal conchae

Ethmoid

Plates	Cribriform plate Crista galli Olfactory foramina Perpendicular plate

Surfaces	Lateral surface Orbital lamina Uncinate process Medial surface Supreme nasal concha Superior nasal concha Superior meatus Middle nasal concha Middle meatus

Labyrinth	Ethmoid sinus ethmoidal foramina Posterior Anterior

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