326 THE 



secondary sexual adaptation. It is intended to make the sexes mutually 

 more attractive, and this tends to draw them together reproductively. 

 But human beauty has other reasons for existence than this, is indeed 

 "its own excuse for being." To this virtue the various pigments of the 

 skin and its appendages, especially the hair, distinctly minister, for they 

 help materially to increase the beauty of the human form. 



As protectors of the sensitive body-protoplasm from excessive sun- 

 light the status of the pigmentation is more in doubt. It is not easy in 

 particular to decide whether the secretion of brown or black pigment 

 which occurs after long exposure to bright sunlight is a sort of degenera- 

 tive reaction or a protective process. In the iris it has evidently the 

 latter function; in the hair of the scalp blackness, on the other hand, 

 would tend to make the brain warmer than were the hairs white. Orna- 

 mental pigmentation tends to occur on the body in places not especially 

 exposed to light, for example on the scrotum. 



In general the whole subject of dermal pigmentation needs more careful 

 working-out in its chemical as well as its histological aspects. 



The Hairs and the Nails are properly parts of the skin or appendages to it. 



Hairs are found nearly all over the body, the palms and soles being 

 marked exceptions. In various places the hairs differ greatly in size and 

 rigidity. In its adult stage, the hair consists of medulla, cortical fibers, 

 and cuticle. The pigment-granules are scattered in the cortical layer. 

 An inner and an outer-root sheath surround the growing hair, the latter 

 being an invagination from part of the epidermis. In the center of the 

 base of the hair when in the follicle is the very vascular papilla. Attached 

 to each follicle is a bundle of smooth muscle-fibers so placed that its 

 contraction pulls the hair into an erect position, as happens in terror. 

 Each follicle receives one nerve-fiber which enters the former just below 

 the duct of the sebaceous gland. Here it divides into two non-medullated 

 fibers which surround the hair-follicle and from this partial or complete 

 ring many varicose fibers extend upward and terminate outside the so- 

 called glassy layer, in some of the brutes in special end-organs (Retzius). 

 The muscles of the hairs are supplied from the gray rami communi- 

 cantes of the sympathetic (Huber). 



From what we know of the structure and the nature of the hairs three 

 functions at least may be noted: protection in various ways, especially 

 from cold and heat; as sense-organs of touch; and ornamentation. 



The nails scarcely need discussion. They are keratinous coverings 

 of the ends of the fingers and toes, extending from the epidermis and 

 continually pushing out at a slow rate by growth at their matrix. They 

 serve to protect the ends of the fingers and toes from injury and render 

 these organs, especially the latter, useful for many purposes which else 

 they could not serve. 



