THE INTEGUMENTARY SYSTEM 



113 



STRUCTURE OF THE HUMAN SKIN 



The skin of man, together with its appendages, hair, nails, teeth, mem- 

 brane bones, and glands, is only about four per cent of the body weight. 

 Like that of other mammals, it consists of two tissues, an outer epidermis 

 and an inner connective-tissue corium. 



A cross section of the epidermis shows under the microscope a many- 

 layered epithelium, which varies greatly in thickness in different parts of 



GERMINATIVUM 



:\ 

 «^ 



SWEAT GLANO'^ 



Fig. 107. — A cross section of the thickened skin of the sole. The stratum corneum is 

 especially thickened on the sole and on the palm of the hand. 



the body. Even where it is thinnest, as for example on the back, at least 

 two layers of cells are distinguishable, an inner, growing stratum germina- 

 tivum and an outer, horny stratum corneum. The cells of the stratimi 

 germinativimi are columnar in shape; those of the stratum corneum are 

 flattened and scale-like. The former are alive and, by their constant 

 proliferation on division planes parallel to the surface of the skin, they 

 make continual additions to the stratum corneum. The living cells in 

 their turn, as by the wearing off of the outer layers they come nearer and 



