536 



ANATOMY OF VERTEBRATES. 



smaller species of Chimpanzee (Tr. niger) the temporal ridges 

 meet, in old males, upon the sagittal line, but rarely develope a 

 crest : the lambdoidal boundary-ridges are better marked. 



Independently of the superiority of size of the Tr. Gorilla 

 over the Tr. niger, the skull of the former, figs. 357 — 359, 

 presents well-marked differences of form, differences in the deve- 

 lopement and proportions of the intermuscular ridges, in the dis- 

 position of certain sutures, and in the structure and proportions of 

 certain teeth. Compared in profile, the skull of both species, 

 figs. 356 and 357, presents a striking difference from that of 

 the Orang, fig. 355, in the prominence of the superorbital ridge ; 

 but the temporal ridges, after their junction upon the frontal, 

 rise, in the Tr. Gorilla, into a strong and lofty sagittal crest, 



which is continued to the 

 lambdoidal crest, the great 

 extent of which masks the 

 posterior convexity of the 

 occiput. The zygoma- 

 tic arch is proportionally 

 much stronger in the Go- 

 rilla, and also differs from 

 that in Tr. niger by the 

 squamosal part being of 

 equal depth with the malar 

 part, and by its having its 

 upper border convex, or 

 produced into an angle 

 instead of being straight 

 or slightly concave. The 

 alisphenoid is longer and narrower in Tr. Gorilla, and contri- 

 butes less to the back wall of the orbit than in Tr. niger, in 

 which it forms a much smaller proportion of that part than in 

 Man. The spheno-maxlllary fissure is not only larger in Tr. 

 Gorilla, but is narrower and more vertical, not angularly bent 

 as in Tr. niger. The extent of the premaxillary bones below 

 the nostril is not only relatively but absolutely less in Tr. 

 Gorilla, and the profile of the skull less convex at that part, 

 or less ' prognathic,' than in Tr. niger. The breadth of the pre- 

 maxillaries and of the incisor teeth is the same in both, whilst 

 in all other dimensions the Tr. Gorilla greatly surpasses the 

 Tr. niger-. this is seen in the height of the sagittal crest, the 

 thickness of the great superorbital bar of bone, the prominence 

 of the ectorbital walls, and of the inferior tumid malar boundaries 

 of the orbits, fig. 358, 26. The nasal bones have united together 



Gorilla (Tr. Gorilla, male), cii 



