CHAPTER X 



LEPUS : A WARM-BLOODED, VIVIPAROUS CHORD ATE 



Externals. — The most obvious characteristic of the rabbit and 

 of other mammals is the possession of hair, which, typically, 

 forms a complete covering to the body. Hairs are more or 

 less cylindrical epidermal structures, seated in little pits or 

 follicles at the base of each of which is a papilla. The 

 epidermal cells just above the papilla multiply actively and 

 contribute new material to the hair, which in this way grows 

 in length (see p. 234). The central axis of the hair is called the 

 medulla, and surrounding this is the cortex (which is often 

 pigmented), and a cuticle. The function of hair is to prevent 

 loss of heat from the body by radiation, for mammals are warm- 

 blooded (homothermous). It also serves for protection, and 

 sometimes as a sensory tactile organ, as in the case of the 

 vibrissas or " whiskers." 



The fingers and toes end in claws, likewise epidermal 

 structures. 



The skin is thicker than in the forms previously described. 

 In the epidermis there is a great difference between the 

 actively-growing cells at the base (stratum Malpighi), and the 

 flat, horny cells on the surface (stratum corneum) which are 

 continually being lost and replaced from the stratum Malpighi. 



The dermis of the skin forms the basis of leather, and it 

 commonly contains fat forming a layer which assists the 

 animal in maintaining its internal heat. Beneath the skin are 

 muscles which serve to move and shake it. In the region of 

 the trunk these muscles form the panniculus carnosus ; in the 

 head the skin muscles are concerned with movements of the 



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