DIGESTIVE ORGANS. 217 



The Tongue. 



The tongue as it occurs in its more primitive condition in the fishes 

 is merely a fleshy fold developed from the floor of the mouth between the 

 hyoid and mandibular arches, the hyoid frequently extending into and 

 supporting it. It is incapable of motion, except as moved by the sup- 

 porting skeleton, for it lacks intrinsic muscles. It is sensory, having 

 both tactile and gustatory functions. It is often papillose, and in a 

 few teleosts it bears teeth (p. 209). 



The tongue in the cyclostomes is considerably different. Here it 

 is thick and fleshy and is supported by a cartilaginous skeleton (p. 75) 

 and is moved by appropriate protractor and retractor muscles at the 

 base, developed from the postotic myotomes and innervated by the 

 hypoglossal nerve. With its terminal armament of epidermal teeth 

 it serves as the boring organ with which the myxinoids obtain entrance 

 into their prey, while in the lampreys it serves as a rasping organ and 

 also as part of the sucking apparatus. 



In the amphibia there is a greater range of structure. In a few 

 anura (aglossa) the tongue is practically absent; in the perennibranchs 

 it is scarcely more advanced than in the fishes, but elsewhere it contains 

 intrinsic muscles and is extremely mobile. It consists of a small basal 

 portion corresponding to the tongue of the fish, to which is added a 

 large glandular part arising between the copula and the lower jaw. 

 This secretes the slime, so useful in capturing the prey. In the anura 

 the tongue is attached at the margin of the jaw, its free end, when at 

 rest, being folded back on the floor of the mouth. In urodeles the base 

 of attachment is more extensive and embraces the anterior margin of 

 the tongue and part of the ventral surface as well. The supporting 

 skeleton (fig. 85) consists of the median portion (copula) with usually 

 two pairs of cornua, largely formed from the ventral ends of the hyoid 

 and first branchial arches (see p. 64). 



The reptilian tongue includes not only the parts found in the am- 

 phibia (the fold above the basihyal), but also a median growth, the 

 tuberculum impar, arising between the basihyal and the lower jaw, 

 and also a pair of lateral folds lying above the first visceral arch 

 (Lacerta). In the turtles and crocodiles the tongue lies on the floor 

 of the mouth and is not protrusible. In the squamata it can be extended 

 from the mouth, and in snakes and many lizards there is a sheath into 

 which it is withdrawn. In many snakes the tongue is two-pointed at the 



