XIV. 



THE SKIN. 



THE apparently complicated structure of the integument 

 becomes easily understood, if we keep in mind that there 

 are but two tissues entering the structure of the skin viz., 

 connective tissue and epithelium. The connective tissue pro- 

 duces the flat layer, called derma ; the epithelium covers the 

 derma on its outer surface. The boundary line between the 

 two formations is not even, but fluted, supplied with numerous 

 small protrusions of the derma, the so-called papillae, the sum 

 total of which bears the name " papillary layer." The bundles of 

 the connective tissue everywhere run an oblique course ; they 

 are arranged in the shape of a coarse reticulum in the lowest 

 portion of the derma, whose rhomboidal meshes contain a vary- 

 ing amount of fat-globules, the so-called subcutaneous tissue. In 

 the derma proper, the bundles run in two main directions, inter- 

 lacing at acute angles, and thus producing a very dense felt, 

 which by being tanned gives the leather. On the lowest portions 

 of the derma the bundles are relatively coarse 5 they become 

 finer nearer the papillary layer, and in the latter very delicate 

 connective-tissue fibers are noticeable only, without a distinct 

 arrangement into bundles. The epithelial formations on the 

 top of the derma, again, exhibit two layers : the lower one, that 

 nearest to the papillary layer, is living, and supplied with nerves, 

 the so-called rete mucosum ; while the outermost layer is com- 

 posed of dry, horny epithelia, giving the formation called epi- 

 dermis. The connective tissue is supplied with blood-vessels and 

 lymphatics j the epithelium lacks such formations. 



