CHAP. V] THE CRANIA OF THE SIMIIDAE (PRIMATES) 221 



above, being separated by these two bones, which join at the pterion. The 

 infra-temporal crest is often represented by a single spinous process. 



The base of the skull shews the foramen magnum in the position charac- 

 teristic of Simiidae, i.e. much nearer the occipital end of the skull than in 

 the Hominidae. The glenoid fossa is shallow, with a moderately developed 

 eudo-glenoid tubercle, and small post-glenoid process. As in the Gorilla, an 

 Eustachian spinous process is common, but the styloid and vaginal processes 

 are absent. The tympanic bone, as in the other Simiidae, is extensive from 

 without inwards and semi-cylindrical in form. The occipital condyles are 

 small and variations in the conformation of the margins of the foramen 

 magnum are rare. 



The mandible is smaller and weaker than in the Orang-utan or the Gorilla, 

 but still massive in comparison with the human jaw. The area for the 

 digestive muscle (anterior belly) is a narrow strip or (in many cases) not to 

 be identified. Posteriorly to the symphysis in the middle line is a deep 

 pit, and at the lower margin of this, neither a ridge nor tubercles are 

 found. 



The dentition presents the usual Catarrhine formula : the canine teeth, 

 except in old males, do not so far surpass the other teeth in bulk, as in Simia 

 and Gorilla. Yet the canines are of very great size in comparison with those 

 of Man, and this is the more remarkable when it is remembered that the 

 molar teeth, in male skulls with such large canines, may fail to attain the 

 dimensions even of European molars. These considerations are of great 

 importance in the study of prehistoric mandibles such as those from Mauer 

 and Piltdown. 



The diastema is less wide in the Chimpanzee than in the other Simiidae. 

 In the reduced size of the third upper molar teeth, and in the small cusps 

 of the molar series, anticipations of the human conditions are present. 

 Slight but distinct crenation of the crowns of the molar teeth frequently 

 occurs. 



In concluding these brief descriptions of the external characters 

 of the skulls of Simiidae, it is convenient to present the main 

 points of diagnosis of the several genera in a tabular form as 

 follows : 



Distinctive features of the skulls of Simiidae. 



I. Hylobates (Gibbon). 



Its small size differentiates it from those of other Simiidae. The 

 skulls of Cercopithecidae of similar size are distinguished by their rela- 

 tively smaller capacity and by the nasal bones (which are longer than 

 in Hylobates). The molar teeth of Hylobates do not possess the two 

 transverse ridges crossing the crown which are so characteristic of the 

 teeth of the lower Anthropoidea. 



