THE GREAT CHIMPANZEE. 419 



In six skulls of Troglodytes niger Prof. Wyman found that " the temporal ridges are 

 generally separated from each other by a space varying from half an inch to one or two 

 inches, according to age, but in none of them is to be seen even a rudiment of the inter- 

 parietal ridge." In the adult, but by the condition of the teeth, not old male Tr. niger, 

 described and figured by nie, the temporal ridges have met above the obliterated suture, 

 and developed the rudiment of an ' interparietal ridge,' which would probably have risen 

 above its rudimental state had the exercise of the large temporal muscles been longer 

 continued. Processes, ridges and crests dependent upon the stimulus of muscular action 

 for their development, are the seats of most variety, and the least safe or satisfactory 

 osteological marks of specific distinction. In the great males of the Tr. Gorilla even a 

 certain range of variety is presented by the skulls of the four adult males, which we are 

 now able to compare. 



In the one described by Prof. Wyman the interparietal or sagittal crest is elevated about 

 1-| inch above the skull, and terminates above in a thin and free edge : in the fine male 

 skull figured, and in the older male's skull, the two temporal ridges, though touching 

 each other at their base, do not coalesce to form a single sagittal crest, but each termi- 

 nates in a free edge, inclining from its fellow, and neither of them rise to half an inch 

 at their highest part, three inches behind their point of contact. 



With regard to the 4th difference, it appears to me that the specific character of the 

 zygomatic arches is best shown by the depth and convex or angular upper contour of 

 the squamosal portion of the arch. 



In respect to the .'Sth difference, Prof. Wyman has well indicated the characteristic 

 forms of the anterior and posterior nares ; and the conformity of the four skulls, two 

 males and two females, submitted to his able and scientific scrutiny, in this important 

 character, with the three skulls which I have described, adds to the confidence in its 

 constancy and value. The observed range of variety does not materially affect the well- 

 marked difference of form in the posterior nares. Prof. Wyman finds in the Tr. niger 

 that " the transverse diameter of the orifice exceeds that of the vertical, but in the Tr. 

 Gorilla the vertical is twice that of the transverse, a condition which results from the 

 elongation downwards of the superior maxillary bones." In one skull of an adult female 

 Tr. niger, in the Bristol Museum, the vertical diameter equals the transverse diameter of 

 the posterior nares, and it exceeds it by about one-half only in the three skulls of the 

 TV. Gorilla in the same museum. 



With regard to the Gth character, which was pointed out to Prof. Wyman by Prof. 

 Agassiz, it is stated that " in the Chimpanzee the infraorbital canal forms a deep groove, 

 terminating in the sphenomaxillary fissure, its depth remaining uniform to its termina- 

 tion ; but in the Enge-ena {Tr. Gorilla) the canal becomes gradually less deep from 

 before backwards, and at the fissure is scarcely obvious." In the skull of the female 

 Tr. Gorilla examined by me, the infraorbital canal is also shorter and shallower than in 

 the skull of a female Tr. niger, but the varieties observable in the condition of this canal 



