484 THE VERTEBRATE SKELETON. 



f rentals to the occipital crest. The orbit is completely encircled 

 by bone, and the alisphenoid assists the jugal and frontal in 

 shutting it off from the temporal fossa, leaving however a 

 communication between the two as the sphenomaxillary fissure. 

 In most cases the frontals meet one another in the middle line 

 between the mesethmoid and orbitosphenoid, but in Man, Simia, 

 and some Cebidae this does not take place. In nearly all 

 Cebidae the parietal and jugal meet one another, separating 

 the frontal and alisphenoid on the skull wall ; in Man and all 

 Old World monkeys, on the other hand, the alisphenoid and 

 frontal meet and separate the jugal and parietal. The pre- 

 maxillae nearly always send back processes which meet the 

 nasals. The palate is rather short and both the palatine and 

 the premaxilla take a considerable part in its formation. The 

 pterygoid plate of the alisphenoid is decidedly large, and there 

 is no alisphenoid canal. There is never any great develop- 

 ment either of the paroccipital process of the exoccipital, or 

 of the postglenoid process of the squamosal. The periotic 

 and tympanic are always fused together ; in Cebidae they 

 form a small bulla, but a bulla is not developed in any Old 

 World forms. The periotic is large, especially the mastoid 

 portion, which forms a distinct portion of the skull wall be- 

 tween the squamosal and exoccipital. In Man and still more 

 in Old World monkeys, the external auditory meatus is drawn 

 out into a definite tube, whose lower wall is formed by the 

 tympanic ; in the Cebidae the tympanic is ring-like. The 

 perforation of the periotic by the carotid canal is always 

 conspicuous. 



The mandible is rather short and broad, and the angle 

 formed by the meeting of the two rami is more obtuse than in 

 most mammals. The coronoid process is fairly well developed, 

 and the angle is more or less rounded. In most Primates the 

 condyle is considerably widened, but this is not the case in 

 Man. In Mycetes the mandible is very large, its ascending 

 portions being specially developed. The hyoid of Primates is 



