OCCIPITAL BOXE. S3 



temporal bone, while the extremity of its basilar process is united to 

 the body of the sphenoid, in the young condition by cartilage, but after 

 the age of twenty years by continuous osseous substance. The rhom- 

 boidal form generally given by the meeting of these borders at the four 

 : angles is not unfrequently somewhat changed to the octagonal, l)y the 

 greater or less projection of subordinate obtuse angles be.tween tlio 

 upper and lateral, and between the lateral and lower angles. 



The tabular portion, or supra-occipital, on its j)o>;ferior surface 

 •presents a rough jiromineuce, the c.rtfrnal occipital profuhrrance, arching 

 outwards from which, on each side, is the superior occipifal rithjc or 

 curved lino, which divides the surface into two parts, the upper, covered 

 by the hairy scalp, convex and uniform ; the lower, uneven, and marked 

 by the impressions of the muscles of the neck which are attached to it. 

 This lower surface is divided into two lateral portions by a median 

 ridge called the external occipital crest or spine, and each of these por- 

 tions is again divided into an upper and a lower surface by the inferior 

 curved line or ridfie, which, after extending some distance outwards, is 

 met by a ridge and groove passing from before backwards. These sur- 

 faces mark the attachments of the rectus capitis posticus major and 

 minor, and of the obliquus capitis superior muscles. 



Tlie deep surface of the bone is marked by two smooth ridges which 

 cross one another, one extending from the upper angle to the great 

 foramen, and the other transversely from one lateral angle to the other, 

 and at the point of intersection of these ridges is the internal occipital 

 ])rotuherance. Separated by these ridges are four hollows, the superior 

 and inferior occipital fossce, which lodge respectively the posterior cere- 

 bral and the cerebellar lobes. The superior and transvei'se ridges are 

 grooved in the course of the longitudinal and lateral venous sinuses 

 respectively. The wider space where those grooves meet at the internal 

 occipital protuberance receives the torcular Herojihili. The inferior 

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

 margins of tlie tabular portion are dee})ly serrated above the lateral 

 angles for articulation with the parietal bones ; below that level, they 

 unite with the mastoid portions of the tenvporal bones. 



The condylar portions or ex-occipitals, bear the articulating 

 condyles on their lower part, close to the margin of the foramen mag- 

 num in its anterior half. The condyles are elliptical and converge iu 

 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 inlcrior 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 vary greatly in size and arc often 

 absent on one or both sides. Externally to the condyle, on each side, is 

 a portion of bone, which is placed over the transverse pi'ocess of the 

 atlas, continuous posteriorly with the tabular part, and anteriorly hav- 

 ing a free excavated margin, the juf/uhir notch, which contributes, with 

 a notch in the temporal bone, to form the foramen lacerum juipdare ; 

 its external extremity projects into the angle between the mastoid and 

 petrous portions of the temporal bone, and is called thcjuf/ular eminence. 

 This process presents inferiorly a rough elevation, which gives attach- 



VOL. I. D 



