92 PROFESSOR OWEN ON THE OSTEOLOGY OF 



slightly roughened longitudinal tract beneath the inner wall of the alveoli of the last 

 two molars in the Gorilla. The foramen or entry of the dental canal is relatively larger 

 in the white varieties of Man than in the Gorilla, and the inner boundary of that fora- 

 men is more produced. The crotaphite fossa is less depressed and less marked in Man. 

 The condyle is more compressed from before backwards in Man, and its articular 

 surface is better defined. The outer surface of the angle of the jaw in the Gorilla has 

 neither the tuberosity nor the vascular groove present in some human jaws. 



In comparison with the lower jaw of the Chimpanzee {Troglodytes nigerY, that of the 

 Gorilla is chiefly distinguished by the superior height and expanse of its ascending rami. 

 The rounded part of the angle is less extensive in the Chimpanzee ; that angle is conse- 

 quently better marked ; and both in this respect, and in the minor vertical extent of 

 the horizontal ramus beneath the last molar tooth, the Chimpanzee approaches nearer 

 the Human subject : but both differences seem to be due to its inferior strength as 

 compared with the Gorilla, and are not particularly characteristic of Man. The 

 symphysis is accordingly relatively deeper in the Chimpanzee ; and though sloping 

 backwards as it descends, it is more angular at its lower part than in the Gorilla. The 

 mental foramen, besides being situated below the socket of the second premolar, is nearer 

 the lower border of the ramus than in the Gorilla, and in so far differs more from Man. 

 The antero-internal ridge of the ascending ramus is more behind, and more distant 

 from, the antero-external ridge than in Man ; but it rises, without the angular bend 

 shown in the Gorilla, and the crotaphite depression is relatively smaller and is less 

 well-defined than in the Gorilla. The smooth, rounded ridge, continued from the 

 middle of the antero-internal ridge to the condyle, is well marked in the old male 

 Chimpanzee. The breadth of the symphysis is almost equal to that in the Gorilla, 

 as is shown in PL XXXII. fig. 3, and is consequently relatively greater, compared with 

 the length of the jaw, than in the Gorilla, the Chimpanzee in this important character 

 departing further from the Human type. 



The entry of the dental canal is nearer the antero-internal ridge, and is relatively 

 lower, in the Chimpanzee than in the Gorilla, which, in the more central position of that 

 foramen, more nearly approaches Man. At the lower and back part of the symphysis 

 there is a fossa, bounded below by a transverse crescentic ridge, or backward continua- 

 tion of the under surface of the centrum. 



The coronoid process agrees with that in the Gorilla in its shape and the backward 

 curve of its apex. The condyle resembles in shape that of the Gorilla, but the 

 articular surface does not extend so far downwards behind, and is better defined there. 

 In two lower jaws of adult specimens of Chimpanzee, the uppermost of the ridges on 

 the inner and back part of the rising ramus is the most developed, as is shown in fig. 5. 

 The form of the posterior margin of that ramus is shown in Man (PL XXXI. fig. 4), 

 in the Gorilla (PL XXXII. fig. 2), and in the Chimpanzee {ib. fig. .5). 



' Trans. Zool. Soc. vol. iii. PI. LVIU. 



