AND AFFINITIES OF THE GORILLA. 259 



character to the Human skull, and to which only the Gorilla, in the Ape-tribe, makes 

 any approximation. 



No Orang, Chimpanzee, or Gibbon shows any rudiment of mastoid processes ; but 

 they are present in the Gorilla, smaller indeed than in Man, but unmistakeable ; they 

 are, as in Man, cellular, pneumatic, and with a thin outer plate of bone. This fact led 

 me, in a former memoir, to express, when, in respect to the Gorilla, I only knew the 

 skull, the following inference, viz. — " from the nearer approach which the Gorilla 

 makes to Man, in comparison with the Chimpanzee or Orang, in regard to the mastoid 

 processes, that it assumed more nearly and more habitually the upright attitude than 

 those inferior anthropoid Apes do'." This inference has been fully borne out by the 

 rest of the skeleton of the Gorilla, subsequently acquired. 



In the Chimpanzee, as in the Orangs, Gibbons, and inferior Simim, the lower surface 

 of the long tympanic or auditory process is more or less flat and smooth, developing in 

 the Chimpanzee only a slight tubercle, anterior to the stylohyal pit. In the Gorilla the 

 auditory process is more or less convex below, and developes a ridge, answering to the 

 vaginal process, on the outer side of the carotid canal. The processes posterior and 

 internal to the glenoid articular surface are better developed, especially the internal one, 

 in the Gorilla than in the Chimpanzee ; the ridge which extends from the ectopterygoid 

 along the inner border of the foramen ovale terminates in the Gorilla by an angle or 

 process answering to that called " styliform " or " spinous " in Man, but of which there 

 is no trace in the Chimpanzee, Orang, or Gibbon. 



The orbits have a full oval form in the Orang ; they are almost circular in the 

 Chimpanzee and Siamang, more nearly circular and with a more prominent rim in the 

 smaller Gibbons ; in the Gorilla alone do they present the form which used to be 

 deemed peculiar to Man. There is not much physiological significance in some of the 

 latter characters, but, on that very account, I deem them more instructive and guiding 

 in the actual comparison. 



The occipital foramen is nearer the back part of the cranium, and its plane is more 

 sloping, less horizontal, in the Siamang, than in the Chimpanzee and Gorilla. Consider- 

 ing the less relative prominence of the fore part of the jaws in the Siamang as compared 

 with the Chimpanzee, the occipital character of that Gibbon and of other species of 

 Hylohates marks well their inferior position in the quadrumanous scale. 



In the greater relative size of the molars, compared with the incisors, the Gorilla 

 makes an important closer step towards Man than does the Chimpanzee. The molar 

 teeth are relatively so small in the Siamang, that, notwithstanding the small size of the 

 incisors, the proportion of those teeth to the molars is only the same as in the Gorilla : 

 in other Gibbons [Hylohates lar), the four lower incisors occupy an extent equal to that 

 of the first four molars, in the Chimpanzee equal to that of the first three molars, in 

 the Siamang equal to that of the first two molars and rather more than half of the 



' Trans. Zool. Soc. vol. iii. p. 409. 



VOL. V. PART IV. 2 M 



