180 



ANIMAL FORMS 



and the body correspondingly long and snake-like ; but in 

 other cases parts of the vertebrae are reduced in number, 

 and the body is rather short and thick. In the frogs and 

 toads this reduction reaches its culmination, for only nine 

 distinct vertebrae are present, the tail vertebrae, correspond- 

 ing to those of the salamanders, being represented by a 

 rod-like bone, the urostyle, made of segments grown to- 

 gether. 



173. Digestive and other systems. In its main characters 

 the digestive tract of the amphibian (Fig. 109) resembles 



bl. 



Ir. 



FIG. 109. Dissection of toad (Bnfo). an., anal opening; a., auricle; U., bladder; 

 duo., duodenum ; Ing., lung ; Ir., liver; pn., pancreas ; ret., rectum ; spl., spleen; 

 St., stomach ; v., ventricle. 



that of the fishes and the squirrel. The mouth is usually 

 large, and the teeth are very small, as in the frog or sala- 

 mander, or are lacking completely, as in the common toad. 

 In many salamanders the tongue, like that of a fish, is fixed 

 and incapable of movement. In most of the frogs and 

 toads it is attached to the front of the mouth, leaving its 

 hinder portion free, and capable of being thrown over and 

 outward for a considerable distance. In the throat region 

 gill-clefts may persist, but they usually close as the lungs 

 reach their development. The succeeding portions of the 

 canal are comparatively straight in the elongated forms, or 



