468 



ZOOLOGY. 



phibians having a middle ear in addition to the internal ear 

 of fishes. In toads and frogs the tongue is quite free and 

 capable of being protruded, except in Pipa and Dadyle- 

 thra, where it is entirely wanting. In other forms the 

 tongue is much as in fishes, not being capable of extension 



from the mouth. As in 

 fishes, there are no salivary 

 glands. The gills of Am- 

 phibians consist of two or 

 three pairs of branched, 

 fleshy appendages, which 

 grow out from as many 

 arches. While in the toad 

 and frog the gills are small 

 and remain but for a short 

 time, in the larval salaman- 

 ders, especially the axolotl 

 (Fig. 430), the gills are still 

 longer retained, while in 

 the mud-puppy {Necturus) 

 they persist throughout life. 

 The digestive canal is us- 

 ually simple, straight, there 

 being no enlargement form- 

 ing a stomach ; in other 

 species, both tailless and 

 tailed, the canal dilates into 

 a stomach, which in the 

 toad lies across the body- 

 cavity. In tadpoles, which 

 live on decaying vegetable 

 matter, the digestive tract 

 is very long and closely coil- 

 ed (Fig. 431). 



The lungs are long, slender sacs, much like those of the 

 Dipnoan Lepidosiren, which extend backwards into the ab- 

 domen, as in the lizards and snakes, no diaphragm existing 

 to confine them in a thoracic cavity. The larynx exists in 

 a very rudimentary state, though the vocal powers of the 



Fig. i^,—AxoloU, or larval Salamander, 

 showiDgthe gills, heart {H), aortic branches 

 and lungB (PA). P, pulmonary arteries ; 

 jo;j, pulmonary veins ; A, bulbus arteriosus 

 from which the vascular arches (B) origi- 

 nate ; bb, branchial vein ; the lower J4, vena 

 cava ; F, descending aorta, — From Gervais 

 et Van Beueden. 



