522 ZOOLOGY SECT. 



line, of the occiput. The par-occipital processes are only re- 

 presented by slight eminences the jugular eminences. There 

 is no auditory bulla ; the mastoid portion of the periotic pro- 

 jects downwards as a prominent mastoid process. The periotic, 

 tympanic, and squamosal early fuse into one bone the temporal 

 bone. The post-glenoid process is very slightly developed. The 

 whole facial region is relatively small. The orbits, which are of 

 moderate size, are directed forwards ; the bony margin is com- 

 plete, and a plate of bone developed partly from the jugal, partly 

 from the alisphenoid, almost completely cuts it off from the 

 temporal fossa, leaving only a small aperture of communication 

 the spheno-maxillary fissure. The frontal suture usually early dis- 

 appears. The nasals rarely become fused. The suture between 

 the premaxillae and the maxillae becomes obliterated at an early 

 stage, so that the entire upper jaw appears to consist of a single 

 bone. A peculiar spine, the nasal spine, is developed in the middle 

 line below the nasal opening. The most marked feature of the 

 mandible is the presence of a prominence, the mental prominence,. 

 in the lower part of the symphysial region ($.). The stylo-hyal 

 nearly always becomes fused, together with the tympano-hyal, to 

 the periotic and tympanic, giving rise to a slender process the 

 styloid process (sh.~) projecting downwards from the base of the 

 skull. 



None of the other Primates have a cranial capacity approaching 

 that of Man ; and those modifications in the shape of the skull, 

 which are the concomitants of the great development of the brain 

 in the human species, are accordingly not recognisable, or are much 

 less strongly marked. The various fossae of the cranium, as a 

 rule, occupy, however, the same relative positions as in Man; the 

 cerebellar fossa is entirely beneath the cerebral; and the ethmoidal 

 plane, and that and the foramen magnum (occipital plane) are 

 usually both horizontal or nearly so. In all the Simiidse, with 

 the exception of the Orang, the frontals meet in the middle line 

 below, over the presphenoid. 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. 1108), 

 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 par-occipital processes are 

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

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

 In the Cebidse and Hapalidas 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 



