392 PROFESSOR OWEN ON THE OSTEOLOGY OF 



§ 4. Comparison of the Slitill of the Troglodytes Gorilla, Savage, with that of the Tro- 

 glodytes niger, Geoff. 



Independently of the superiority of size of the Tr. Gorilla, the sexual difference in 

 respect of which is greater in that large species than in Tr. niger, there are well-marked 

 differences of form, differences in the development and proportions of the intermuscular 

 ridges, and, what is more decisive of specific distinction, in the disposition of certain 

 sutures and in the structure and proportions of certain teeth. Compared in profile, as in 

 Plates LVIII. and LXI., the skulls of both species present the striking difference from 

 thetwoOrangs (vol. ii. Pis. XXXI. and XXXIII.) in the prominence of the supraorbital 

 ridge ; but this is greater in the Tr. Gorilla, and occasions a deeper concavity below it, 

 the vertical prominence descending from the middle of the supraorbital ridge being 

 more marked. The temporal ridges, after their junction upon the frontal, rise into a 

 strong and lofty sagittal crest, which is continued to the lambdoidal crest. This is 

 enormous in the Tr. Gorilla, and, with the zygomatic process, renders all the posterior 

 and lateral parts of the calvarium concave. The same extent of the lambdoidal crest 

 masks or rather destroys the posterior convexity of the occiput in Tr. Gorilla, so that in 

 the direct side view of the cranium only the outline of the large mastoid cells appears at 

 this part. The foramen auditorium externum being of the same size as in the Tr. niger, 

 is relatively smaller in the Tr. Gorilla. The zygomatic arch is proportionably much 

 stronger in the large Chimpanzee, and also differs from that in Tr. niger by the squamosal 

 part (27) being of equal depth with the malar part (26), and by its having its upper border 

 convex or produced into an angle instead of being straight or slightly concave. The ali- 

 sphenoid ( 6 ) is longer and narrower in Tr. Gorilla, and contributes 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-maxiliary fissure is not only larger in Tr. Gorilla, but is nar- 

 rower and more vertical, not angularly bent as in Tr. niger. The extent of the premax- 

 illary 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. 



More important differences appear on comparing the two skulls in a front view (Plates 

 LIX. and LXII.). The breadth of the premaxillaries (22) 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 supraorbital 

 bar of bone, the prominence of the ectorbital walls (12, 26', PI. LXII.), and of the inferior 

 tumid malar boundaries of the orbits. But the decisive specific character is given by 

 the form and connections of the nasal bones. These have coalesced together in Tr. 

 Gorilla as in Tr. niger, but less completely, the median suture remaining along the 

 lower half (is, PI. LXII.). The coalesced upper portions of the nasals (15') ascend higher 

 above the nasal processes of the maxillary than in Tr. niger, become contracted between 



