Lateral parts of occipital bone 4615436 224659802 2008-07-09T21:17:01Z Jonathan Cardy 4071608 disambig Atlas {{Infobox Bone | Name = Lateral parts of occipital bone | Latin = pars lateralis | GraySubject = 31 | GrayPage = 131 | Image = Gray131.png | Caption = [[Occipital bone]] at birth. | Image2 = Gray130.png | Caption2 = Occipital bone, inner surface. | System = | MeshName = | MeshNumber = | }} 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]] 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 (anatomy)|atlas]] when the head is bent backward; the floor of this fossa is sometimes perforated by the [[condyloid canal]], through which an emissary vein passes from the [[transverse sinus]]. Extending lateralward from the posterior half of the condyle is a quadrilateral plate of bone, the [[jugular process]], excavated in front by the [[jugular notch]], which, in the articulated skull, forms the posterior part of the [[jugular foramen]]. The jugular notch may be divided into two by a bony [[spicule]], the intrajugular process, which projects lateralward above the hypoglossal canal. The under surface of the jugular process is rough, and gives attachment to the [[Rectus capitis lateralis]] muscle and the [[lateral 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 the [[Atlas (anatomy)|atlas]]. Laterally the [[jugular 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 to [[Ossification|ossify]]. The upper surface of the lateral part presents an oval eminence, the [[jugular tubercle]], which overlies the [[hypoglossal canal]] and is sometimes crossed by an oblique groove for the [[glossopharyngeal]], [[vagus]], and [[accessory nerve]]s. On the upper surface of the jugular process is a deep groove which curves medialward and forward and is continuous with the [[jugular notch]]. This groove lodges the terminal part of the transverse sinus, and opening into it, close to its medial margin, is the orifice of the [[condyloid canal]]. {{Gray's}} {{Skull}}