122 ELEMENTARY ANATOMY. [LESS. 



certain of the auditory ossicles, as we shall see more distinctly 

 when we come to treat of the organs of sense. 



Confining ourselves to man's own class, his mandible 

 appears to be well developed, but the form and proportion 

 of its parts may be very different from what we see in him. 



Thus there may be, as in the Great Ant-eater and Ceta- 

 ceans, no representative of the ascending ramus ; or it may 

 be very low, as in most Rodents, e.g. the Porcupine. 



The coronoid process may be much developed, rising 

 greatly above the condyle, affording attachment to the volu- 

 minous temporal muscle, as in the Dog ; or it may be low 

 or rudimentary, as in many Rodents. 



A considerable process, termed the angular process, may be 

 developed at the point of junction of the posterior borders of 

 the vertical ramus with the inferior margin of the horizontal 

 one, as in the Dog. This process may be distinctly bent in- 

 wards, as in the Opossums and almost all Marsupials. 



The condyle is always either more or less eo'nvex or 

 flattish (thus differing from the surface offered by the 

 articular part of the lower jaw in animals below Mammals, in 

 which it is always more or less concave), but its longer 

 diameter may be antero-posterior, as in some Rodents, or 

 still more decidedly transverse than in man, as in carnivorous 

 animals, where the movement of the jaw is vertical and not 

 to and fro, whether from before backwards, as in Rats, 

 Rabbits, &c., or from side to side, as in Ruminants. 



Mostly in Mammals the lower jaw continues throughout 

 life to be made up of two bones articulating at the symphysis 

 by suture as in the human infant at birth. 



The symphysis generally inclines from above downwards 

 and backwards, and only in one Ape (the Siamang Gibbon) 

 is there a chin as in man. 



The symphysis may be exceedingly narrow, as in the 

 Ant-eater and Porpoise. It may be very elongated but hori- 

 zontal, as in the Cachalot. The two rami may be each nearly 

 straight, or each may be strongly curved outwards, as in the 

 Whalebone Whales. 



The symphysis may be narrow and grooved above so as 

 to give it the appearance of a spout, as in the Elephant, or 

 it may be extraordinarily produced downwards, as in the 

 Dugong. 



The entrance of the dental foramen may be exceedingly 

 capacious and funnel-shaped, as is the case in the Dolphin. 



The mandible may be directly connected with the neural 



