CHAPTER X 



CHARACTERS OF THE CLASS MAMMALIA — THE RABBIT 



Before examining a Rabbit, as an example of the highest 

 class of Vertebrates — the Afam/nalia, it \\'\\\ be well to re- 

 capitulate some of the characters of the frog, the organisa- 

 tion of which is higher than that of a fish. 



The frog, taken as an example of the class Amphibia, differs 

 from a fish in the following points, amongst others. Its 

 paired limbs have not the form of paddle-like fins, the fore- 

 limb consisting of upper arm, fore-arm, wrist and hand, and 

 the hind-limb of thigh, shank, ankle, and foot, each with 

 its characteristic skeletal parts ; it has no median fin in 

 the adult, and that of the tadpole is not supported by fin- 

 rays ; there is no hard, dermal exoskeleton ; respiration in the 

 adult is pulmonary, and internal nostrils are present ; there 

 are two auricles in the heart, and the cardinal veins are 

 replaced by a postcaval ; there is a urinary bladder formed 

 as an outgrowth of the cloaca. Moreover the skeleton, 

 unlike that of the dogfish, is in the adult composed mainly 

 of bone. 



In all these characters the frog resembles the rabbit. But 

 the Mammal differs from the Amphibian in many important 

 respects, some of the chief of which are : — the presence o 

 an epideri?iic exoskeleton consisting of hairs ; the high 



