264 



"\-ei;tebrate animals. 



tail, and breathes M-holly Ijy lungs, and through the skin. Both 

 l)aiis of limbs are always dev'elo])ed in the full-grown animal, and 

 the hinddinibs are usually considerably longer tlian the fore-limbs, 

 and generally liave the toes Avebbed, whilst those of the fore-limljs 

 ■are free. The skin is soft, and there are rarely any ti'aces of any 

 integumentary skeleton. The sj)inal column is short ; the dorsal 

 vertebr;e are very long ; and the rilis are (juite rudimentary, their 

 [ilace being taken by greatly-developed transverse ]irocesses. The 

 bodies of the vertebrae are hollow in front and conve.K behind {pra- 

 coslom). The bones of tlie fore-arm (radius and idrui), and those of 

 the sliank {tihiii and fihtila), are united together to form single bones. 

 The upper jaw is usuall}' furnished with teeth, and the lower jaw 

 sometimes, but there are no teeth in the Toads. The lungs are well 

 developed, comparatively sjjeaking ; and as there are no ribs by 



Fig. 1S3.— Til 



iiinon Frng (/?(')((-/ t^iirporarh). 



which the cavity of the chest c:in bo ex|ianded, the air is taken 

 into the lungs b)- a jiroeess nearly akin to that of swallowing. There 

 c;in be im doubt, also, that the skin plays .a very imp(n'tant pa.rt in 

 the aeration of the bicjod, and that the fi-ogs especially can airry on 

 (heir i'espir;itii>n Ijy nie.-uis of the skin withimt the assistance of the 

 lungs for :i very leiigtlienc<l perind. This, hdwever, .should not lead 

 to any ci'edeiice being given to the often-repeated stiiries of frogs and 

 toads being finnid in chised cavities in snlid rock, no authenticated 

 inst;ince of such an occurrence being known to science. The ova of 

 the frogs .-11111 toads arc <leiiosited, in m.-isses or strings, in water, and 

 the young oi' l;ir\-a' are fauiili.-ir to every one as tadpoles. ITj)on its 

 escape from the egg, the youug fi'o.; (tig. I S4) iiresciits itself as a 

 litth; lisli-like cre.'iture with a broa.d head, .a sac-like belly, and a 



