Chap. XVIII] 



THE SKIN 



349 



Sebaceous glands. — The sebaceous glands are small, saccular 

 glands, which lie between the hairs and their arrector muscles. 

 They occur everywhere over the skin surface, with the exception 

 of the palms of the hands and the soles of the feet. 



Each gland consists of a collection of small tubes overspread 

 with a network of capillaries. From the gland a small duct as- 

 cends, and opens either upon the surface of the skin or, as is more 



SUBCUTANEOUS 

 AREOLAR TISSUE 



DUCT OF 



SEBACEOUS 



GUND 



T— ROOT OF HAIR 



HAIR FOLLICLE 



— -ADIPOSE TISSUE 



BULB OF HAIR 

 PAPILLA OFHAIB 



ARRECTOR MUSCLE 



Fig. 173. — Vertical Section of the Skin, showing Sebaceous Glands, 

 Sweat-glands, Hair, and Follicle, also Arrector Muscle. (Gerrish.) 



common, into a hair follicle. Their size is not regulated by the 

 length of the hair. Thus, some of the largest are found on the 

 nostrils and other parts of the face, where they often become en- 

 larged with pent-up secretion. 



Sebum. — The secretion of the sebaceous glands is called sebum. 

 It contains fats, soaps, epithelial cells, albuminous matter and 

 inorganic salts. It serves to remove waste matters and is classed 

 as an excretion, but its more important purposes are to keep the 

 skin and hair soft and pliable, and to form a protective layer on 



