AND AFFINITIES OF THE GORILLA. 277 
(Simia Troglodytes, Linn., Troglodytes niger, Geoffr.), characterized by less long arms 
(reaching to the knee), a long thumb of the hind hand, never without ungual phalanx 
and nail, reaching to the second joint of the second toe: the ligamentum teres is present ; 
there are thirteen pairs of ribs; the superorbital ridge is strongly developed; the 
tuberculate grinding surface of the molars is smooth; the premaxillaries become 
anchylosed during the first or deciduous dentition. According to the above generic 
characters, the Gorilla belongs to the genus Troglodytes. 
But equal value has been given to other characters, e. g. Ist, ‘‘ to the much-elongated 
and much-depressed form of the head, and to the very prominent cranial crests, in the 
adult’.” 
These, however, are sexual rather than generic characters ; they are present only in 
the adult males, and require a certain age of such adult to bear the terms in which 
they are expressed by Is. Geoffroy. As compared with aged adult male specimens of 
Troglodytes niger, they are differences, not of kind, but simply of degree. This degree 
of development of the cranial crests, with their concomitant influence on the shape of 
the head, moreover, accords with the difference in the size of the adult males of the 
Chimpanzee and Gorilla. 
In every admitted natural genus of Carnivorous Unguiculates, the small species differ 
from the large species, just as the small kind of Troglodytes does from the large one, in 
the degree of development of the intermuscular plates of bone affording attachment to 
the temporal muscles. 
2. ‘‘ The external ear is small and of the human shape’.”” It is smaller in proportion 
to the head, and a little smaller absolutely, in the Gorilla than in the Chimpanzee: in 
both, the auricle is broader in proportion to its length than in Man: the space between 
the helix and anthelix at their upper part is much less than in Man ; and the fossa of the 
anthelix is scarcely marked : the lobulus is rather better marked in the Gorilla (Pl. XLVII. 
fig. 6) than in the Chimpanzee; and this is the only notable difference in the conch or 
external ear of the two Apes, except size: it is a difference which, in my judgment, is 
of a specific, not generic value. 
The third alleged generic distinction, viz. the greater relative length of the upper 
limbs®, rests, as has been already shown’, on an error of observation. 
The small amount of difference may help the specific diagnosis: in the degree in 
which it is determinable, it places the Gorilla higher in the genus than the Chimpanzee. 
‘ « La Gorille n’appartient point au genre Troglodytes: il constitue un genre distinct. Les caractéres prin- 
cipaux de ce genre peuvent étre ainsi résumés :— 
“1, Téte arrondie dans le jeune age; téte tres-allongée et trés-déprimée 4 l’état adulte: les crétes craniennes 
trés-saillantes ’’ (Isid. Geoffroy St.-Hilaire, op. cit. p. 38). 
» «2. Conques auriculaires petites et de forme humaine ” (ib., op. cit. p. 38). 
* «3, Membres antérieurs longs; leur extrémité atteignant, l’animal étant debout, le milieu de la jambe ” 
(ib., op. cit. p. 38). ‘ 
* Compare Memoir, No. VIL., pl. 13. fig. 2 (Gorilla), with Memoir, No. I., pl. 48 (Chimpanzee). 
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