232^ Zoological Society. 



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 TV. 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 Dr. 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 terminates 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. 



4. The specific cliaracter of the zygomatic arches is best shown 

 by the depth and convex or angular upper contour of the squamosal 

 portion of the arch. 



5. Dr. 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 scru- 

 tiny, in this important character, w^th the three skulls which I have 

 described, adds to our 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. Dr. Wyman finds in the 

 TV. niger that " the transverse diameter of the orifice exceeds that 

 of the vertical, but in the TV. 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 

 Trogl. 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 Tr, Gorilla in the same museum. 



6. With regard to the sixth character, which was pointed out to 

 Dr. Wyman by Prof. Agassiz, it is stated that " in the Chimpanzee 

 the infraorbital canal forms a deep groove, terminating in the spheno- 

 maxillary fissure, its depth remaining uniform to its termination ; but 

 in the Enge-ena {Trogl. Gorilla) the canal becomes gradually less 

 deep from before backwards, and at the fissure is scarcely obvious." 

 In the skull of the female Trogl. Gorilla (fig. 2) examined by me, 

 the infraorbital canal is also shorter and shallower than in the skull 

 of a female Trogl. niger, but the varieties observable in the condition 

 of this canal in different individuals of the Trogl. niger are more 

 marked than those above noticed in the skulls of the two specie** and 

 induce me therefore to attach less importance to this character as a 

 specific one. In two skulls of adult males, e. g. in the College of 

 Surgeons, the infraorbital groove as it passes backwards again be- 

 comes a canal by the meeting, and in one specimen by the coalescence 

 of the two sides of the groove above the canal for an extent of from 

 two to three lines before it enters the spheno-maxillary fissure. Dr. 

 Wyman indeed notices a similar conformation in an adult cranium 

 of the Chimpanzee belonging to Dr. J. C. Warren. Now this is a 



