176 
ZOOLOGY, 
because they live a part of their lives in the water. All 
Amphibians, with very rare exceptions, pass through a 
metamorphosis; the young or larvae are called tadpoles; 
their form is fish-like, as they breathe by external gills, and 
do not at first have legs. 
An examination of the skeleton shows that the skull re- 
sembles that of the higher vertebrates in being composed 
of few pieces, while there are short ribs, and a true shoulder 
and pelvic girdle to which the limb-bones are joined. The 
Fig. 223.— Skeleton of a Frog, a, skull; 6, vertebrae; c, sacrum, and e, its con- 
tinuation (urostyle); /, suprascapula; g, humerus; 7i, fore-arm bones; t, 
wrist-bones (carpals and metacarpals); d, ilium; wi, tlaigh (femur); n, leg- 
bone (ulna) ; o, elongated first pair of ankle-bones (tarsals) ; p, g, foot-bones 
or phalanges. After Owen. 
heart is 3-chambered, there being two auricles and one 
ventricle. 
Like fishes, Batrachians are highly colored in the spring 
during the breeding season. The males of the newts at 
this time acquire the dorsal crest and a broader tail-fin, 
while in some species prehensile claws are temporarily de- 
veloped on the fore-legs of the male. Male toads and frogs 
are musical, the females being comparatively silent; the 
vocal organs of the male are more developed than in the 
females, and iu the European edible frog large sacs for 
