IN THE LOWEU ANIMALS, ETC. 333 



of the lower jaw is much flattened laterally (Fig. 

 55, c), and the glenoid cavity is prolonged in the 

 antero-posterior direction, or in the same axis 

 with the jaws; thus limiting the action in mastica- 

 tion to a to-and-fro motion. (Fig. 56, g.) 



The effect of this longitudinal direction of the 

 glenoid cavity is greatly increased by the position 

 of the condyloid and coronoid processes, which 

 rise very little above the level of the grinding 

 surface of the molars. 



The jaws, therefore, do not possess the free 

 lateral motion of the sheep, and they present a 

 striking contrast to those of the tiger. (See Figs. 

 32 and 33.) If the articulation in the latter 

 animal may be compared to a powerful hinge, 

 admitting of vertical motion only, the jaws of the 

 capybara more nearly resemble the sliding action 

 of a bolt in its frame. 



A beautiful provision for the stability of the 

 transverse plates is seen in the grooved sides 

 of the alveoli ; the projecting transverse plates 

 fitting into these groves, they receive efficient 

 support against the strain to which the antero- 

 posterior motion would otherwise expose them. 



We may also observe in the form of the skull 

 a special adaptation to set this curious dental 

 apparatus in action. 



The temporal fossa, as in the Carnivora, is con- 

 tinuous with the orbit, and an elongated process 

 arises from the maxillary bone, connecting it with 



