CHAPTER XII. 



FIG. 63. 



THE SKIN. 



THE skin serves integumentary and protective purposes, is 

 an important excretory organ, is the seat of sensory terminals, 

 and possesses other functions. It consists of two parts, a 

 thin outer epithelial layer, the epidermis or cuticle, and a 

 thicker, lower connective-tissue layer, the cutis vera, or corium. 

 Beneath it is a variable layer of subcutaneous tissue. The 

 skin contains numerous glands of two kinds, sudoriparous 

 and sebaceous, and also the hairs and nails; these are all 

 derived from, or modifications of, the epidermis. 



The epidermis, the thinner outer layer of the skin, consists 

 of stratified squamous epithelium, and is of epiblastic origin. 

 It varies in thickness and the 

 development of its parts in 

 different situations. It is 

 divisible, in the first place, into 

 two sharply distinct layers, an 

 outer, hard, horny, layer, and 

 a lower, soft protoplasmic 

 layer, the " rete mucosum." 

 Each of these is again divisi- 

 ble into other strata, which 

 are, from the surface down- 

 ward, the stratum corneum 

 and stratum lucidum, making 

 up the horny portion, the 

 stratum granulosum and stra- 

 tum Malpighii, making up the 

 rete mucosum. In addition, 

 the lowermost layer of (co- 

 lumnar") cells in the Mai- Section of skin, showing sweat-gland, a, 



,7 stratum corneum; 6, rete mucosum; 



pighian Stratum IS almost dlS- c, corium ; d, subcutaneous tissue. 



tinct enough to be differen- 

 tiated as a special layer. These layers may be exhibited thus : 



151 



