| Lateral parts of occipital bone | |
|---|---|
 Human skull seen from above (parietal bones removed.) Lateral parts of occipital bone shown in red. | |
 Occipital bone, inner surface. Lateral parts shown in red. | |
| Details | |
| Identifiers | |
| Latin | pars lateralis ossis occipitalis |
| TA98 | A02.1.04.009 |
| TA2 | 556 |
| FMA | 52859 |
| Anatomical terms of bone | |
Thelateral parts of theoccipital bone (also called theexoccipitals) are situated at the sides of theforamen magnum; on their under surfaces are thecondyles for articulation with the superior facets of theatlas.
The condyles are oval or reniform (kidney-shaped) in shape, and their anterior extremities, directed forward and medialward, are closer together than their posterior, and encroach on thebasilar portion of the bone; the posterior extremities extend back to the level of the middle of theforamen magnum.
The articular surfaces of the condyles are convex from before backward and from side to side, and look downward and lateralward.
To their margins are attached the capsules of theatlantoöccipital articulations, and on the medial side of each is a rough impression or tubercle for thealar ligament.
At the base of either condyle the bone is tunnelled by a short canal, thehypoglossal canal (anterior condyloid foramen).
This begins on the cranial surface of the bone immediately above theforamen magnum, and is directed lateralward and forward above the condyle.
It may be partially or completely divided into two by a spicule of bone; it gives exit to thehypoglossal or twelfthcerebral nerve, and entrance to a meningeal branch of theascending pharyngeal artery.
Behind either condyle is a depression, thecondyloid fossa, which receives the posterior margin of the superior facet of theatlas when the head is bent backward; the floor of this fossa is sometimes perforated by thecondyloid canal, through which an emissary vein passes from thetransverse sinus.
Extending lateralward from the posterior half of the condyle is a quadrilateral plate of bone, thejugular process, excavated in front by thejugular notch, which, in the articulated skull, forms the posterior part of thejugular foramen.
The jugular notch may be divided into two by a bonyspicule, the intrajugular process, which projects lateralward above the hypoglossal canal.
The under surface of the jugular process is rough, and gives attachment to theRectus capitis lateralis muscle and thelateral atlanto-occipital ligament; from this surface an eminence, the paramastoid process, sometimes projects downward, and may be of sufficient length to reach, and articulate with, the transverse process of theatlas.
Laterally thejugular process presents a rough quadrilateral or triangular area which is joined to the jugular surface of the temporal bone by a plate of cartilage; after the age of twenty-five this plate tends toossify.
The upper surface of the lateral part presents an oval eminence, thejugular tubercle, which overlies thehypoglossal canal and is sometimes crossed by an oblique groove for theglossopharyngeal,vagus, andaccessory nerves.
On the upper surface of the jugular process is a deep groove which curves medialward and forward and is continuous with thejugular notch.
This groove lodges the terminal part of the transverse sinus, and opening into it, close to its medial margin, is the orifice of thecondyloid canal.
This article incorporates text in thepublic domain frompage 131 of the 20th edition ofGray's Anatomy(1918)
