222 THE CRANIA OF THE SIMIIDAE (PRIMATES) [SECT. A 



II. Simia (Orang-utan). 



Distinguished by its absolute size from the skull of Hylobates. 

 Distinctions from Chimpanzee and Gorilla : 



(a) The supra-orbital ridge for each orbit is distinct and the two 

 ridges are not continuous across the forehead. 



(6) The nasal bones are reduced to mere splints. The facial profile 

 is often concave (simognathic), and though some crania of Chimpanzee 

 and Gorilla present this character in a slight degree, it is never so marked 

 in them as in Simia. 



(c) The crowns of the molar teeth are crenated, and consequently 

 the cusps are obscured. 



(d) The mandible is, relatively to the rest of the skull, of large 

 dimensions. 



III. Anthropopithecus (Chimpanzee). 



Distinguished by its absolute size from the skull of Hylobates. 

 Distinctions from Simia are as indicated in Section II. 



(a) The supra-orbital ridges are continuous across the forehead. 



(b) The nasal bones though flat and short are laminar and not 

 splint-like. 



(c) The crowns of the molar teeth bear distinct, but not very large 

 cusps. 



(d) The mandible is relatively smaller. 



The following are the distinctions between the crania of Chimpanzee 

 and Gorilla. 



(a') The skull of the Chimpanzee is smaller, the cranial part is 

 relatively larger, and not characterized by such large ridges as the skull 

 of Gorilla. 



(b') The nasal bones are shorter (not extending far below the level 

 of the inferior orbital margins), and their outer margins are more nearly 

 parallel to one another than in Gorilla. 



(c') The nasal aperture tends to be pyriform in contour. 



(d r ) The molar teeth are much smaller and bear less prominent 

 crowns. But the incisor teeth are sometimes larger than those of the 

 adult Gorilla, though all the other teeth are smaller than in that animal. 



IV. Gorilla. 



The skull is distinguished by its actual size from that of Hylobates. 

 The following are the features distinguishing the skull of the Gorilla 

 from that of the Orang-utan. 



(a) As in Anthropopithecus, the supra-orbital ridges are continuous 

 across the forehead. 



