702 PRIM A TES 



approximation to man, and the same is true with regard to the 

 occipital production, which is most developed in Chrysothrix. Most 

 of the Simiidce exhibit, however, a distinct convexity of the occiput, 

 and thereby differ markedly from the Cercopithedda, in which this 

 region is flat. The rotundity of the cranium is obscured in the 

 larger Apes, such as the Orang (Fig. 353) and Gorilla, by the 

 development of prominent bony ridges for muscular attachment ; 

 these attaining their maximum in the males of the species last 

 named, where the sagittal crests and the supraorbital ridges are 

 very prominent. The mastoid process is always smaller in the 

 Apes than in Man, and as it diminishes in size the petrosal tends 

 to assume an inflated or bullate condition. The orbits in shape 

 are most like that of Man in the Gorilla ; and, in accordance with 

 the size of the eyes, they are of enormous dimensions in Nyctipithecus. 



The angle formed by the plane of the foramen magnum with 

 that of the basicranial axis is subject to variation according to the 

 degree of convexity of the occiput, but is generally smaller than in 

 Man, although larger in Chrysothrix. There is an external bony 

 meatus auditorius in Man, the Simiidce, and the Cetcopithecidce, but 

 none in the Cebidce and Hapalidce. 



The premaxillse of the Apes are always large ; and, except in 

 the Chimpanzee, the premaxillo-maxillary suture persists until after 

 the permanent dentition has been developed. The nasals are 

 smaller and flatter than in Man, but are largest in Mycetes. The 

 two rami of the mandible are invariably completely ankylosed at 

 the symphysis in the adult. The Siamang (Hylobates syndactylus) is 

 the only ape in which the mandibular symphysis shows a slight 

 projection in front corresponding to the human chin. In Mycetes 

 the angle of the mandible attains an enormous development (Fig. 

 338) to protect the huge inflated basihyal. The frontal sinuses, 

 though present in the Simiidce, are generally replaced in the 

 Cercopithecidce by a coarse diploe, but they are present in the 

 Cebidce and Hapalidce, being especially large in Cebus. In fully 

 adult individuals the cranial sutures become obliterated, the inter- 

 nasal suture disappearing at an early age in the Simiidce and most 

 of the Cercopithecidce. As in many Carnivora, the tentorium, or 

 membrane separating the cerebrum from the cerebellum, may 

 become ossified in some of the American forms. 



The number of the teeth in the Old World Apes is invariably 

 the same as in Man, namely i f , c ^, p f , m f, total 32 ; but in the 

 Cebidce the cheek-teeth are p f , m f , and in the Hapalidce p f , m f . 

 It is probable that the two pairs of incisors correspond to the first 

 and third of the typical series of three. In all Apes the dental 

 series is interrupted by a diastema, and the canines of the males 

 are large. Man alone has an uninterrupted dental series of a 

 horse-shoe-form, without prominent canines. 



