538 ZOOLOGY SECT. 



the pre-sphenoid. In many monkeys the outer surface of the 

 cranium is smooth and free from prominent ridges ; but in the 

 Baboons, the Orangs, the Gorilla, and the Chimpanzee (Fig. 1189) 



FIG. 1189. Skull of Chimpanzee (Anthropopithecus troglodytes). (After Blainville . 



there are strongly developed occipital, sagittal, and supra-orbital 

 ridges, usually much more prominent in the male than in the female, 

 and increasing in size with age. The paroccipital processes are 

 always rudimentary, but there are well-marked post-glenoid pro- 

 cesses. The mastoid does not form a distinct mastoid process. 

 In the Cebidae and Hapalidee alone is there a tympanic bulla. 

 The entire facial region is relatively larger than in Man ; the pre- 

 maxillo-maxillary region is always more prominent, and in the 

 Baboons projects forwards as a distinct muzzle. The orbit is 

 separated from the temporal fossa as in Man. The nasals are usually 

 ankylosed in the adult. The nasal spine is never developed. The 

 suture between the premaxilla and the maxilla only becomes 

 obliterated, if at all, in old individuals. The mental prominence 

 of the mandible is never developed, the anterior surface of the 

 symphysial region sloping backwards and downwards from the 

 bases of the incisor teeth. The stylo-hyal never gives rise to an 

 ossified styloid process. 



In the skull, as in many other respects, the Lemurs occupy an 

 intermediate position between the higher Primates and the lower 

 orders of Mammals. The occipital and ethmoidal planes are 

 usually vertical. The tympanic forms a large bulla. The orbits, 

 which are large, are usually separated from the temporal fossae 

 only by a narrow rim of bone. The lacrymal foramen is situated 

 on the face outside the margin of the orbit. The facial region 

 is usually elongated, and may form a prominent muzzle. 



In all the Primates the clavicle is present and complete, and 



