180 ANIMAL FORMS 
and the body correspondingly long and snake-like; but in 
other cases parts of the vertebre 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 vertebre are present, the tail vertebre, 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 
Fie. 109.—Dissection of toad (Bufo). an., anal opening ; aw., auricle ; b/., bladder ; 
duo., duodenum ; ing., lung ; /7., 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 
