THE CHIMPANZEES AND ORANGS. 93 



In the lower jaw of the adult male Orang-utan {Pithecus Satyrus, var. WurmbUy the 

 first difference is the lower and more obtuse coronoid process ; next, the more full 

 elliptical form of the condyle, due to its greater antero-posterior breadth ; then the 

 stronger development and lower origin of the antero-external ridge of the ascending 

 ramus, and the greater breadth of the channel dividing it from the antero-internal ridge : 

 this ridge rises straight to join the external one at the fore part of the coronoid process. 

 Behind it the crotaphite depression is deeper but narrower than in the Gorilla. The 

 external crotaphite depression is also better marked. 



The dental foramen, by its relatively higher position than in the Chimpanzee, 

 corresponds closer with that in Man. Behind and below it one or two ' mylohyoid ' 

 grooves extend in the direction of the canal. The mental foramen is nearer the lower 

 border of the jaw than in the Gorilla ; it is below the second premolar tooth. 



The symphysis is broader, flatter, and less sloping at its upper half; below this it 

 is convex and receding, as in the Gorilla. There is a slight prominence at its under 

 part, on each side of which a rough tract extends outwards for nearly two inches. A 

 fossa, bounded below by a rough tract or ridge, characterizes the lower and back part 

 of the symphysis. A narrow linear ridge extends from behind the last alveolus forwards 

 and downwards — a feeble trace of the internal oblique ridge in Man. Five or six rough 

 ridges on the inner side and back part of the ascending ramus, with intervening de- 

 pressions, indicate the attachment of the pterygoid, as in the Gorilla. The angle of the 

 jaw is better marked in the Orang. The alveolar part of the jaw is shorter in propor- 

 tion to the rami in the Orang. The same characteristic distinction from Man is shown, 

 as in the Gorilla and Chimpanzee, by the straightness and parallelism of the molar series. 



In the lower jaw of a female Pithecus Satyrus, the anterior and posterior borders of 

 the ascending ramus are nearly straight and parallel. 



Hyoid Arch. 



This arch, in the Gorilla, offers some well-marked peculiarities and distinctions from 

 that in Man. The basihyal is relatively much larger : it is more deeply excavated be- 

 hind, with the aperture directed towards the glottis: the opposite convexity is raised. 

 The outer surface of the thin osseous walls is smooth, save at its lower and lateral part, 

 which shows marks of muscular insertions. There was no trace of lesser cornu or cera- 

 tohyal : the thyrohyal or greater cornu is long and nearly straight, diminishing in 

 thickness as it approaches the thyroid. The stylohyal is relatively shorter than in Man, 

 and does not become anchylosed to the base of the skull in the adult Gorilla. 



VertebrcB of the Trunk. 



The vertebral column of the trunk in the Gorilla differs from that of Man in showing 

 but one gentle curve, with the concavity forwards, from the sacrum to the cervical 



' Trans. Zool. Soc. vol. i. PI. LIII. 



