CHORDATA. 



3 2 3 



of the epidermis is usually columnar in form, and from this 

 .layer the outer cells are renewed, and all special epidermal 

 growths arise (Fig. 153, c.e). The dermis consists largely 



FIG. 153. Diagram of the skin in Mammals, showing the multiple layered condition, 

 together with outgrowths and ingrowths. Drawn by Dr. J. W. Folsom. E, epidermis; 

 D, dermis; a, adipose tissue, fat deposited amid the connective tissue; b, blood vessels; 

 c.e., columnar epithelial layer of the epidermis; f, hair follicle; h, hair; n, nerve; .<?., 

 nerve ending (sensory corpuscle); p, pore of sweat gland; seb., sebaceous or oil gland 

 of hair; s.g., sweat gland; s.c., horny layer of epidermis; s.m., mucous layer of 

 epidermis. 



Questions on the figure. What suggests that the columnar layer of 

 the epidermis is the most vitally important layer? Are the hair and glands 

 dermal or epidermal growths? Which structures found in the dermis 

 seem to be invasions of that layer by outside structures? What are the 

 functions of the various layers of the skin ? Which parts are ectodermal 

 and which mesodermal in origin ? 



