2() 



THE SKKLKTOX 



ance, is soon. Tho vortical ridge runs ujiwards to the superior angle of the bone 

 and furnishes attachment for the falx cerebri; the portion of the ridge below the 

 1 irotuboranco, tho internal occipital crest, is for tho falx cerebelli. As it approaches 

 tho foramen magnum tliis ridge divides, becoming lost upon its margins. The 

 auirlo of divorgonce is sometimes occupied by a shallow fossa for the extremity of 

 the vermiform ]»rocess of the cerebellum, and is called the vermiform fossa. The 

 liorizontal ridge is deeply grooved; to the edges of the groove the tentorium cere- 

 liolli is attached; the grooves lodge the greater part of the lateral sinuses. To one 

 side of the internal occipital protuberance, usually tho right, the furrow for the 

 sinus is deeper and frequently forms a circular fossa Avhich receives the torcular. 

 This fossa is sometimes exactly in the middle line. 



The squamo-occiintal has three angles and four borders. The superior angle 

 tits into the space formed by the union of the two parietals. Tho lateral angles 

 mark the external limits of the middle nuchal lines, and occupy the angle formed 

 bv the parietal and mastoid ])ortion of tho petrosal on each side. The ridge 



Fig. 31. — Occipital Bone, Cerebral Surface. 



SUPERIOR ANGLE 



FOR SUPERIOR LONGITUDINAL 

 SINUS AND FALX CEREBRI 



CEREBRAL FOSSA 



GROOVE FOR LATERAL SINUS 



LATERAL ANGLE 



CEREBELLAR FOSSA 



GROOVE FOR LATERAL SINUS 



JUGULAR PROCESS - 

 FOR PETROSAL 



BASI-OCCIPITAL 



between the su]H'rior and lateral angles is tho superior border ; it is serrated 

 deeply, and artictilatos with the posterior border of tho parietal to form the lamb- 

 doid suture. Tho inferior border extends from the lateral angle to the jugular 

 process ; it articidatcs with tlie mastoid portion of the petrosal. 



Tho ex-occipitals form the lateral boundaries of the foramen magnum. The 

 lateral surface of oaih ox-occipital is extended outwards to form a (juadrilatoral 

 buttress of bone, the jugular process. This has an outer rough surface for articu- 

 lation with the jugular surface of the petrosal. Its anterior border is doo])ly notched 

 to form the posterior lioundary of the jugtdar foramen, and the notch is directly 

 continuous with a groove on the upper surface which lodges the termination of tho 

 lateral sinus. Its under surface gives attachment to the rectus capitis lateralis antl 

 the olili({ue occipito-atlantal ligament. The pneumatic mastoid colls occasionally 

 extend into this process. Ixaroly a process of bone projects from its under surface 

 and represents the paroccipital process present in many manunals. The rest of the 

 ex-occipitals enter into the formation of the condyles, and will be separately de- 

 scribed. 



