The lateral parts of the occipital bone
are situated at the sides of the foramen magnum; on their under surfaces are the condyles for articulation with the superior facets of the atlas.
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 the basilar portion of the bone; the posterior extremities extend back to the level of the middle of the foramen 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 the atlantoöccipital articulations
, and on the medial side of each is a rough impression or tubercle for the alar ligament
At the base of either condyle the bone is tunnelled by a short canal, the hypoglossal canal
(anterior condyloid foramen).
This begins on the cranial surface of the bone immediately above the foramen 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 the hypoglossal
or twelfth cerebral nerve
, and entrance to a meningeal branch of the ascending pharyngeal artery
Behind either condyle is a depression, the condyloid fossa
, which receives the posterior margin of the superior facet of the atlas
when the head is bent backward; the floor of this fossa is sometimes perforated by the condyloid canal
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