THE BONES OF THE HEAD 59 



the right, there is a wide depression, at which point the longitudinal 

 groove is continued into the corresponding lateral groove. This 

 depression lodges the torcular HerophUi, which is a dilatation 

 formed where the superior longitudinal sinus bends sharply to 

 become continuous with the right lateral sinus. The four fossae 

 are arranged in a superior pair, called superior occipital or cerebral, 

 and an inferior pair, called inferior occipital or cerebellar. Each 

 cerebral fossa presents a number of digitate impressions for the 

 convolutions of the occipital lobe of the cerebrum, which is lodged 

 in it. The cerebellar fossae, which are separated by the internal 

 occipital crest, are smooth, but may show transverse striations. 

 They are much thinner than the cerebral, and lodge the hemispheres 

 of the cerebellum. 



The angles are superior and two lateral. The superior angle 

 forms the highest part of the bone, and fits in between the postero- 

 superior angles of the parietals. The lateral angles are situated at 

 either end of the transverse ridge on the internal surface. 



The borders are two superior and two inferior. Each superior 

 border extends from the superior angle to the lateral angle, and is 

 serrated for the posterior border of the corresponding parietal. Each 

 inferior border extends from the lateral angle to the jugular process, 

 and is faintlv serrated for the mastoid portion of the temporal. 



The basilar process (basi-occipital) is a compressed quadrilateral 

 mass, which projects forwards and upwards in front of the foramen 

 magmmi. Its superior surface presents a broad median depression, 

 called the basilar groove, which is sloped dovs-nwards and back- 

 wards to the foramen magnum, and lodges the medulla oblongata. 

 At either side of this groove there is a narrow groove for the inferior 

 petrosal venous sinus The inferior surface presents at its centre 

 the pharyngeal tubercle for the fibrous raphe of the phar^Tix. On 

 either side of this tubercle there is a rough, oblique impression for 

 the insertion of the rectus capitis anticus major, and between the 

 outer part of this impression and the foramen magmun the surface 

 gives insertion to the rectus capitis anticus minor. The anterior 

 border is thick, rough, and truncated, and up to the twentieth 

 year it articulates with the body of the sphenoid by synchon- 

 drosis, but thereafter ankylosis takes place. The posterior border, 

 which is thin, smooth, and concave, bounds anteriorly the foramen 

 magnum, and sometimes presents a third occipital condyle of small 

 size for articulation with the tip of the odontoid process of the axis. 

 This border gives attachment to the middle odontoid or suspensory 

 ligament. Each lateral border is thick and rough for the petrous 

 portion of the temporal. 



The condylar portions (exoccipitals) are placed on either side of the 

 foramen magniun, where they extend as far back as its posterior 

 margin, and very nearly as far forwards as its anterior margin. 

 Each bears on its under surface a condyle. The condyles are oval, 

 convex, and covered by cartilage, and they articulate with the 

 superior articular processes of the atlas. Their long axes are 



