AND AFFINITIES OF THE GORILLA. 277 



(Simla 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. 1st, " 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 aflbrding attachment to 

 the temporal muscles. 



2. " The external ear is small and of the human shaped" 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. Lea caracteres prin- 

 cipaux de ce genre peuvent etre ainsi resumes : — 



" 1 . Tete arrondie dans le jeune age ; tete trfes-allongee et tr^s-de'primee a I'etat adulte : les cretes craniennes 

 tres-saillantes " (Isid. Geoffroy St.-Hilaire, op. cit. p. 38). 



' "2. Conques auriculaires petites et de forme humaine " (ib., op. cit. p. 38). 



• " 3. Membres antdrieurs longs ; leur extrdmit^ atteignant, 1' animal etant debout, le milieu de la jambe " 

 (ib., op. cit. p. 38). 



* Compare Memoir, No. VII., pi. 13. fig. 2 (Gorilla), with Memoir, No. I., pi. 48 (Chimpanzee). 



2 o2 



