784 



lower surface of the long tympanic or auditory process is smooth and flat, or slightly concave, 

 in Tr. niger, and developes a slight tubercle anterior to the stylohyal pit : in the Tr. Gorilla 

 the same process is more or less convex helow, 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 Tr. Gorilla, than in the Tr. niger : the ridge which extends 

 from the ecto-pterygoid along the inner border of the foramen ovale terminates in Tr. Gorilla 

 by an angle or process answering to that called ' styliform ' or ' spinous ' in Mail, but of which 

 there is no trace in the Tr. niyer. 



The palate is narrower in proportion to its length in the Tr. Gorilla, but the pre!iiaxi!lsry 

 portion is relatively longer in Tr. niger. Two anterior palatine foramina, one on each side 

 the almost confluent incisive foramina, are more constant and conspicuous in Tr. Gorilla : the 

 posterior palatine foramina are nearer the posterior border of the bony palate in the Tr. niyer. 

 The pterygoid fossse are relatively deeper and longer in the Tr. niger. The posterior nares 

 are deeper or longer in proportion to their breadth in Tr. Gorilla ; and the posterior border 

 of the bony palate is emarginate at its middle, instead of being produced backwards into a 

 point as in Tr. niyer. 



As decisive marks of specific distinction as any of those deducible from the forms, pro- 

 portions and connections of the bones are presented, in the Tr. Gorilla, by the greater 

 relative dimensions of the canine and molar teeth as compared with the incisors, and by 

 the more complex grinding surface of the last molar and its equality of size with the 

 first molar. The transverse extent of the four incisors of the upper jaw is as great in the 

 Tr. niger as in Tr. Gorilla : the interspace between the right and left canines is even greater, 

 as is also the extent of the diastema between the canines and the incisors of the upper jaw in 

 Tr. niger. The median incisors are, however, larger in proportion to the lateral ones in 

 Tr. Gorilla. 



The crown of the canine is more inclined outwards in Tr. Gorilla ; the anterior inner 

 groove is much deeper ; the base of the posterior trenchant border is more produced ; the 

 ridge between the two inner grooves is more prominent, and the hinder inner groove is con- 

 tinued more decidedly upon the fang in the Tr. Gorilla. 



The last molar of the Tr. Gorilla is more nearly equal to the penultimate one than in 

 Tr. niger, being only slightly narrower across the back part : it has the posterior outer cusp, 

 and particularly the posterior inner cusp, much more distinctly developed, and there is a 

 distinct connecting ridge between the posterior outer and the anterior inner cusps, as in the 

 first molar, and which ridge is not developed in the last molar of the Tr. niger. 



On a review of the differences pointed out in the preceding comparisons, the stronger zygo- 

 inatic arches, with the more developed sagittal and larubdoidal crests, might be viewed as 

 adaptive developments concomitant on the presence of larger canines, and indicative of a 

 larger and more powerful variety of Chimpanzee ; but the larger proportional molars and the 

 smaller proportional incisors, the more equal and complex ultimate molar tooth, together with 

 the prominence of the nasal bones at their median line of coalescence, and above all, the 

 reappearance of the premaxillaries upon the face above the nostril with their longer enduring 

 sutures, constitute a series of differential characters of more importance than such as are due 



