132 Physiology. 



The Dennis. The dermis consists chiefly of tough, 

 interlacing fibers. Hence the strength and durability of 

 leather, which is the dermis preserved and prepared. The 

 epidermis is usually removed in tanning. The dermis is 

 richly supplied with blood capillaries and lymph capillaries^ 

 but the epidermis has neither. 



Papillas. The outer surface of the dermis has many 

 conical elevations, each of which is called a papilla. Over 

 most of the skin they do not show on the outer surface, as 

 the epidermis fills in the spaces between them, but is, itself, 

 smooth on the outside. On the palms and soles the papillas 

 are in rows, and these rows are indicated by the ridges. 



Hairs. Hairs are outgrowths of the epidermis, but are 

 deeply embedded in the dermis. They are supplied with 

 blood at the tip of the root, where the growth takes place. 

 The exposed part of the hair does not contain blood and is 

 not sensitive. (See Fig. 64.) 



Hair-muscles. There are small muscles connected with 

 the roots- of the hairs, by which the hair may be slightly 

 moved. In the lower animals this power is much more 

 used, as when the hair is made to stand erect on the back 

 or tail of an angry cat or dog. The action of these muscles 

 when frightened is what gives a peculiar feeling in the 

 scalp, and to express strong fright we say, " It made his 

 hair stand on end." 



Oil Glands. The oil glands of the skin are distributed 

 over all the surface except the palms and soles. The oily 

 matter is usually poured out around the hairs as they 

 emerge from the skin ; but some of the ducts open on the 

 skin away from a hair. The oil serves to soften the skin 

 and hair and keep them from becoming too dry. (See 

 Fig. 64.) 



