482 THE VERTEBRATE SKELETON. 



PRIMATES. The characters of the skull differ greatly in 

 the two suborders of Primates, the Anthropoidea and the 

 Lemuroidea. 



In the LEMUROIDEA the general relative proportions of the 

 cranium and face are much as in most lower mammals, and the 

 occipital plane forms nearly a right angle with the basicranial 

 axis. The postorbital processes of the frontals are commonly 

 continued as a pair of ridges crossing the roof of the cranium 

 and meeting the occipital crest. Though the postorbital bar 

 is complete, the orbit and temporal fossa communicate freely 

 below it. The lachrymal canal opens outside the orbit, and the 

 lachrymal forms a considerable part of the side of the face. 

 The tympanic is developed into a large bulla. The hyoid 

 apparatus much resembles that of the Dog. 



In the ANTHROPOIDEA the skull differs greatly from that in 

 the Lemuroidea. The cranial portion of the skull is very 

 large as compared with the facial portion, though the 

 comparative development varies, some monkeys, such as the 

 baboons (Cynocephali) having the facial portion relatively large. 

 The comparative size of the jaws does not vary inversely with 

 the general development of the animal, some of the Cerco- 

 pithecidae having comparatively larger jaws than some of the 

 Cebidae. The great size of the cranial part of the skull is 

 mainly due to the immense development of the cerebral fossa, 

 which commonly completely overlaps the olfactory fossa in 

 front, and the cerebellar fossa behind. This development also 

 has the effect of making the ethmoidal and occipital planes lie, 

 not at right angles to the basicranial axis, but almost in the 

 same straight line with it. This is, however, not always the 

 case, as the Howling Monkey (Mycetes) and also some of the 

 very highest monkeys, the Gibbons (Hylobates\ have the occi- 

 pital plane nearly vertical to the basicranial axis. In adult 

 Man the basi-occipital, exoccipitals and supra-occipital coalesce, 

 forming the so-called occipital bone ; while the basisphenoid, 

 presphenoid, alisphenoids, orbitosphenoids and pterygoids form 



