AMPHIBIANS. 339 



head, the next to the aorta, while the venous blood is sent 

 to the lungs. 



In the larvae of the frogs and toads the mouth is small 

 and the horny jaws are adapted to scraping small plants 

 from submerged objects. Correlated with this vegetable 

 food is an extreme length of intestine, it being a notice- 

 able fact that herbivorous animals require a longer diges- 

 tive tract than carnivorous forms. 



In the larvae there is also a well-developed lateral-line 

 system (p. 300), and this persists to some extent in the 

 adult of the aquatic salamanders, though disappearing in all 

 other forms. 



The vertebral column varies greatly in length, and in all 

 except the footless forms it can be divided into neck (cer- 

 vical), breast (thoracic), sacral, and caudal or tail regions, 

 the sacral being that which connects with the pelvic 

 girdle. In some the bodies of the vertebrae are amphicoe- 

 lous (p. 292) ; in most salamanders they are opisthoccelous 

 (rounded in front, hollow behind), while in the frogs and 

 toads they are procoelous (hollow in front). The trans- 

 verse processes of the vertebrae are different from anything 

 in fishes in that thev arise from the neural arch and not 



*/ 



from the centrum. In some forms the ends of these 

 processes are jointed, and from this and other facts they 

 must be regarded as in part equivalent to ribs. It is to be 

 noticed that these ribs never reach the sternum (p. 293), 

 which, by the way, is a structure lacking in all fishes. 



A noticeable feature in the Amphibia is the metamor- 

 phosis during growth, the chief features of which have 

 already been mentioned (p. 337), the result being that 

 the adult differs very considerably from the young. 



All living Amphibia live either in fresh water or on the 

 land; none occur in salt water. The existing forms are 



