230 PHYSIOLOGY OF THE DOMESTIC ANIMALS. 



In the chelonians the hyoid cartilage is of variable shape, but in the 

 main resembles somewhat the hyoid bone of the bird, and is moved by a 

 somewhat similar mechanism, excepting that the conic-hyoid muscles are 

 not wrapped around the hyoid arches. The tongue in this species is 

 muscular and glandular, but not extensible. 



In the saurians (especially in the crocodiles) the tongue resembles 

 that of the chelonians in its slight degree of mobility, and the hyoid 

 bone has a somewhat similar shape. In some saurians the tongue is 

 glandular, in others very muscular and quite extensible. 



Most of the ophidians have the tongue hidden in a sac, non-glandu- 

 lar, and composed of the union of two muscular cylinders which become 

 separate at the tip, forming the well-known forked tongue of serpents. 

 The tongue is proportionately long and extends some distance down 

 beneath the trachea. The posterior extremity of the sac terminates in 

 two cartilaginous plates, which unite anteriorly and constitute the hyoid 

 arch. By means of muscles which originate from the lower jaw and first 

 ribs, and which are inserted in the hyoid arch, the tongue is extruded 

 from the mouth. 



The tongue of the batradiians, with the exception of the salamanders, 

 differs greatly from that of other reptiles. Its anterior extremHy is 

 convex and is fixed to the arch of the chin, while its posterior extremity 

 is free. To be extended from the mouth it must be reversed, and it is 

 the posterior tip which is extruded, while it is withdrawn by a reversal 

 of this motion. These movements are accomplished by the contraction 

 of the genio-glossus and hyo-glossus muscles, the only ones which have 

 any connection with the tongue. 



In quadrupeds, although in some cases we find a special contrivance 

 for the seizing of food, as in the trunk of the elephant, the snout of the 

 tapir, the long tongue of the giraffe, and the extensible, viscid tongue 

 of the ant-eater, the teeth are the chief organs of prehension, aided by 

 the lips and, in some cases, the tongue. Such animals as may stand 

 erect on their hind legs, as the squirrel, bear, and kangaroo, use their 

 fore legs for holding food and bringing it to the mouth, but never use 

 one of them alone. Clawed animals make use of their feet in securing 

 prey, but the food is conveyed to the mouth by movements of the head 

 and jaws. In the rhinoceros the upper lip is prolonged into a finger-like 

 point, which in these animals, as well as in the dromedary, is the prin- 

 cipal organ of prehension of food, 



In man and monkeys the distinguishing prehensile organs are 

 found in the hand, and we find that the first office that the hand instinct- 

 ively performs in both species is to carry food to the mouth. 



Therefore, according to the mode of life for which an animal has 

 been formed, we observe a variety in the arrangement of parts destined to 



