THE OCCIPITAL BONE. {J3 



ridges is the internal occipital protuberance. Separated by the ridges are four hollows, 

 the superior and inferior occipital fossce, which lodge respectively the posterior 

 cerebral and the cerebellar lobes. The superior part of the longitudinal and the 

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

 sinuses respectively. The wider space where the longitudinal groove is continued 

 into one of the lateral grooves (more frequently the right) by the side of the internal 

 occipital protuberance lodges the torcular Herophili. The inferior part of the 



SUP. OCC. FOSSA 



INT. OCC. PROT. 



INF. OCC. FOSSA 



LAT.SULCUS 

 JUG.PROC. 



JUG. NOTCH 

 POST. COND. FOR. 



F. PETR. SULC'JS 



Fig. 



BASiLAR PROC. 



33. OCCIPITAL BONE, FROM BEFORE. (Drawn by D. Gunn.) 



longitudinal ridge is sharp, and is named the internal occipital crest. The margins 

 of the tabular portion are deeply serrated above the lateral angles for articulation 

 with the parietal bones ; below that level, they unite with the mastoid portions of 

 the temporal bones. 



The condylar portions bear the articulating condyles on their lower part, close 

 to the margin of the foramen magnum in its anterior half. The condyles are 

 elliptical, and converge somewhat in front ; their surfaces are convex from behind 

 forwards and from side to side, and somewhat everted. On the inner side of each 

 is a rough impression for the attachment of the lateral odontoid ligament of the 

 axis. Perforating the bone at the base of the condyle is the anterior condylar 

 foramen, running from the interior of the cranium immediately above the foramen 

 magnum outwards and forwards, and transmitting the hypoglossal nerve. Behind 

 the condyle is a pit, posterior condylar fossa, containing usually the posterior condylar 

 foramen ; this gives passage to a vein, but it varies greatly in size, and is often 



VOL. II. D 



