328 



COMPARATIVE ANATOMY 



tongue of Fishes is not capable of movement apart from the 

 visceral skeleton, and is wanting in a proper musculature. It is 

 provided with papillae and serves only as a tactile organ, or, when 

 provided with teeth (e.g. certain Teleosts, Fig. 69), as a pre- 

 hensile organ also. In Dipnoans the tongue is not more highly 

 differentiated than in many other Fishes. 



Amphibians. In Perennibranchiata and young larvse of 

 Myctodera the tongue is very similar to that of Fishes, and is 

 comparable only to a small posterior and median part of the 

 definitive tongue of the latter group : the larger, anterior, 



glandular part is a new forma- 

 tion, and is not represented in 

 Fishes. 



The definitive tongue is very 

 similar in many Urodeles and 

 Anurans, although various dif- 

 ferences are seen in its mode of 

 development in the two groups. 

 Thus in Anura the primitive 

 tongue persists for a much 

 Dorter titne, and is connected 

 on the floor of the mouth with 

 the more anterior, larger, second- 



ary part in a different way; the muscles are earlier developed 

 and more numerous, and the glands appear very late. In general 

 the tongue is more highly differentiated . in Anurans than in 

 Urodeles in consequence of functional adaptation connected with 

 catching the prey. 1 



The surface of the tongue is velvet-like, owing to the numerous 

 papillae, and its mobility varies greatly in the different forms. It 

 is usually attached only by the anterior end (Fig. 239) or by a 



DIFFERENT POSITIONS. 



FIG. 240. HEAD OF Spelerpes fuscus, WITH THE TONGUE EXTENDED. 



portion of its ventral surface: in other cases it is free all round, 

 and in Spelerpes (Fig. 240) is capable of being extended far out 

 of the mouth by means of a complicated mechanism. 



Reptiles. The tongue of Reptiles reaches a much higher 

 ,-stage of development than that of Amphibians. As in them, its 



1 The rapid movements of the Frog's tongue are effected by the genioglossus 

 and hyoglossus muscles, the former acting as a protractor and the latter as a 

 retractor, while the intrinsic muscles are responsible for gripping the prey. In 

 .the Aglossa (Pipa and Xenojnis) the tongue has .undergone degeneration. 



