THE CRANIAL SKELETON. 



Again, it may be divided into two parts, its upper portion 

 being reckoned as a distinct bone (interparietal} as, e.g., very 

 often in Rodents. A still more divided condition of the supra'- 

 occipital may obtain, as in the Ganoid fish Lepidosteus. 



On the other hand, as in the Frogs and Toads, the supra- 

 occipital may be absent altogether, the lateral portions, or 

 exoccipitals, meeting as well above as below the foramen 

 magnum. 



The faintly marked superior curved lines of the human 

 occiput are but feeble representations of the great bony pro- 

 jections which the occipital bone may develop. Thus, even 

 in one of the forms nearest to man/ the Gorilla there maybe 

 an enormous lambdoidal ridge. In Ruminants, again, this 

 ridge may be largely de- 

 veloped, and have bony ex- 

 tensions (the horns) reaching 

 out from it, as in the Ox. 



The jugular process of man 

 may be developed to a much 

 greater extent, bearing the 

 name of par-occipital or para- 

 mastoid process, as e.g. in the 

 Babirussa and Capybara. It 

 may help to form the tym- 

 panic cavity, as in Birds, or be 

 completely absent, as in the 

 Ichthyopsida. 



A singular relationship 

 seems often to exist between 

 an aquatic habit and defect- 

 ive development of the basilar 



part of the occipital bone. Thus this part is altogether absent 

 in Batrachians, it is often imperfectly ossified in Seals, and 

 seems to be rudimentary in some of the Cetacea. 



In the last-named animals, as also in very many I 

 the supra-occipital is brought into direct connexion with the 

 frontal a condition very different from that of man. 



20. Whereas the occipital bone of man is the representative 

 of four distinct bones in lower animals, his PARIETAL bone, 

 on the contrary, is in its normal condition, as it arises always 

 from a single ossification. Indeed, not only is it never mon 

 complex than in him, but in many animals (e.g. the MOJ 

 tremes, Serpents, and the Salmon) the two panetals anchylo: 

 at a very early period into a single, median bone. 



II 2 



FIG. 96. SIDE VIEW OF THE SKULL 

 OF AN ADULT MALE GORILLA. 



o, supra-orbital ridge ; s, sagittal ridge 

 (a lofty plate as indicated by the 

 shading) ; /, lambdoidal ridge the 

 last is foreshortened as it projects 

 laterally. 



