232 Zoological Society. 
Processes, ridges and crests dependent upon the'stimulus of muscular 
action fof 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 présented 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 11 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 pent 
three inches behind their point of contact. 
4. 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. 
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, with 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 
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 
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 Engé-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 Trog/. niger, but the varieties observable in the condition — 
of this canal\in different individuals of the ZJrogl. niger are more 
marked than those above noticed in the skulls'‘of the two species 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 
