CHAPTER XI 



CHARACTERS OF THE CLASS MAMMALIA THE RABBIT 



BEFORE examining a rabbit, as an example of the 

 highest class of Vertebrates the Mammalia, it will be 

 well to recapitulate some of the characters of the frog, 

 the organisation 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, 

 but the fore-limb consists of upper arm, fore-arm, wrist, 

 and hand, and the hind-limb of thigh, shank, ankle, and 

 foot, each with 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 exo- 

 skeleton ; 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 endoskeleton, 

 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 of an epidermic exoskeleton consisting of 



hairs ; the high temperature of the blood, which remains 



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