EXCRETION 475 



The sebaceous glands are simple and compound racemose glands 

 ppening by a common excretory duct on the surface of the epidermis or 

 t into the shaft of a hair-follicle (Fig. 2 14) . These glands are extremely numer- 

 ous and found in all portions of the body, with the exception of the palms 

 :of the hands and soles of the feet, and most abundantly in the face. They 

 ;are formed by a delicate structureless membrane lined by polyhedral 

 i epithelium. 



The sebum is not produced by an act of true secretion, but is formed by 

 a proliferation and degeneration of the gland epithelium. When first 

 poured on the surface, the sebum is oily and semiliquid in character, but 

 soon hardens and acquires a cheese-like consistence. It serves to lubri- 

 cate the hair and skin and prevent them from becoming dry and harsh. 



The surface of the fetus is generally covered with a thick layer of seba- 

 ceous matter, the vernix caseosa, which possibly keeps the skin in a normal 

 condition by protecting it from the effects of the long-continued action of 

 the amniotic fluid in which the fetus is suspended. 





