104 ZOOLOGY. 



extended over the outer surface of the body. The internal 

 portion of the general tegumentary membrane is called 

 MHfOOtM an uiln-ane, and the external portion *////. 



207. Sfr/'rf /(/' <>/' tin- Xkin. -Two principal layers 

 compose the skin : the dermis or true skin, and the epidermis 

 or scarf skin. 



The dermis forms the deeper and thicker layer of the in- 

 teguments. It is a strong, supple, elastic membrane, whitish, 

 and very resistant. A great number of fibres may be seen 

 in it, crossing each other in all directions. Beneath it is a 

 dense layer of cellular substance connecting it to the subjacent 

 parts, and in this sometimes fleshy fibres are found. On its 

 surface may be seen, especially in the palms of the hands and 

 extremities of the fingers, the elevations, called papillae, 

 arranged in regular rows. Of the dermis of animals leather 

 is made. 



The epidermis is a kind of insensible varnish laid over the 

 sensitive skin beneath. It is a tissue composed of dried-up 

 utricules, which form on the surface of the dermis, and which 

 harden only by being exposed to the air. It is composed of 

 several layers, of which the lower or deepest layer, being soft 

 and containing the pigmentary matter giving the colour to 

 the skin, has been viewed and described by some physiologists 

 as a distinct membrane, under the name of rete mucosum. In 

 man, and in many animals resembling him, the epidermis is 

 cast off in the form of small scales, which are constantly 

 renewed. In serpents, the entire epidermis is cast off as a 

 slough. 



The pores of the skin correspond to the summits of the 

 papillae just described. They give passage to the perspiration 

 or sweat, an acid liquid formed by secretion, and which must 

 not be confounded with the insensible perspiration. These 

 pores, exceedingly minute, do not traverse the skin; they an- 

 merely the orifices of the excretory canals of so many small 

 ampulla? lodged in the substance of the skin, and which are 

 the secreting organs of the sweat. 



Other larger orifices are found on the surface of the skin ; 

 some for the passage of the hairs, and others for the escape 

 of a fatty matter secreted by follicles lodged in the substance 

 of the skin. These are called sebaceous glands or follicles. 



208. The principal use <>t' the epidermis is to throw 

 obstacles in the way of evaporation, and to protect th 





