702 PRIMATES 
approximation to man, and the same is true with regard to the 
occipital production, which is most developed in Chrysothriz. - Most 
of the Simide exhibit, however, a distinct convexity of the occiput, 
and thereby differ markedly from the Cercopithecide, 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 Chrysothriz. There is an external bony 
meatus auditorius in Man, the Simide, and the Cercopithecide, but 
none in the Cebide and Hapalide. 
The premaxille 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 A/ycetes. 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 Simiidw, are generally replaced in the 
Cercopithecide by a coarse diploé, but they are present in the 
Cebide and Hapalide, 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 Simiidw and most 
of the Cercopithecide. 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 7 3, ¢ 4, p 3, m 3, total 32; but in the 
Cebide the cheek-teeth are p 3, m 3, and in the Hapalidw p 3, m 2. 
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. 
