OCCIPITAL BONE. 31 



an upper and a lower surface by the inferior curved line or ridge, which, 

 after extending some distance outwards, is met by a ridge and groove passing 

 from before backwards. These surfaces mark the attachments of the rectus 

 capitis major and minor, and of the obliquus capitia superior muscles. 



The deep surface of the bone is marked by two crucial smooth ridges, one 

 extending from the upper angle to the great foramen, and the other trans- 

 versely from one lateral angle to the other, and at the point of intersection 

 of these ridges is the internal occipital protuberance. Separated by these 

 ridges are four hollows, the superior and inferior occipital fossae, which lodge 

 respectively the posterior cerebral and the cerebellar lobes. The superior and 

 transverse ridges are grooved in the course of the longitudinal and lateral 

 venous^ sinuses respectively. The space where those grooves meet at the in- 

 ternal occipital protuberance receives the torcular Herophili. The inferior 

 ridge is single, and is named the internal occipital crest or spine. The 

 margins of the tabular portion are deeply serrated above the lateral angles 

 for articulation with the parietal bones, and, below that level, with the 

 mastoid portions of the temporal bones. 



The CONDYLOID PORTIONS bear the articulating condyles on their inferior 

 surface, close to the margin of the foramen magnum. The condyles are so 

 placed, that a line touching their posterior extremities would cross the 

 middle of the foramen magnum. They are elliptical and placed obliquely 

 so as to converge in front ; their surfaces are convex from behind forwards 

 and from side to side, and slightly everted. Their inner borders are 

 rough, and receive the insertion of the odontoid ligaments of the axis. 

 In front and to the inside of the condyles are the anterior condyloid 

 foramina, which pass forwards and outwards from the interior of .the 

 cranium, and transmit the hypoglossal nerves. Behind the condyles are 

 two pits, containing usually the posterior condyloid foramina ; each of 

 these gives passage to a vein ; but they are often absent on one or both 

 sides. Externally to the coudyle, on each side, is a portion of bone, 

 which is placed over the transverse process of the atlas, continuous pos- 

 teriorly with the tabular part, and anteriorly having a free excavated 

 margin, the jugular notch, which contributes with a fossa in the temporal 

 bone to form the foramen lacerum jugulare ; its external extremity pro- 

 jects into the angle between the mastoid and petrous portions of the 

 temporal bone, and is called the jugular eminence. This process presents 

 inferiorly a rough elevation, which gives attachment to the rectus capitis 

 lateralis muscle ; and superiorly a deep groove for the lateral sinus before 

 it terminates in the jugular notch. 



The BASILAR PROCESS projects forwards and upwards into the middle of 

 the base of the skull. It increases in thickness and diminishes in breadth 

 towards its extremity. Inferiorly it gives attachment to the rectus capitis 

 anticus major and minor muscles and the fibrous band of the pharynx. Its 

 superior surface presents a smooth depression, the basilar groove, which 

 supports the medulla oblongata, and close to each lateral margin a slight 

 grooved mark, which indicates the place of the inferior petrosal sinus. 



Varieties. The upper and lateral angles vary greatly in the degree of their acute- 

 ness. The upper borders are subject to considerable variation, from the presence 

 of ossa triquetra. The condyles vary greatly in size, prominence, and convexity, 

 and are often somewhat unsymmetrical. In some old subjects there is a mark at the 

 back of the foramen magnum, where the occiput rests on the posterior arch of the atlas. 

 Occasionally there is a projection downwards from the jugular process, resembling 

 the descending lateral process found in most mammals. 



