190 



SKELETON AND MUSCLES 



Epidermis 



lerve 



apilla 



pap 



the epidermis. The amount and kinds of pigment deter- 

 mine whether a person is of light or dark complexion, 

 white, black, or yellow. These inner cells are constantly 

 crowing new cells to replace the cells which scale off. 



The nails and the hair arise in the outer layer of the 

 skin. Other structures which arise in the same way are 



the scales of fishes and 

 snakes, the hoofs and 

 horns of cattle, and the 

 feathers of birds. 



The inner layer of the 

 skin is the dermis, and 

 contains blood vessels, 

 nerves, connective tissue, 

 the sweat glands, and 

 sense organs of touch. It 

 is estimated that there 

 are over two million sweat 

 glands in the skin of a 

 man. Their work is to 

 eliminate waste sub- 

 stances from the blood and to keep the body temperature 

 normal (98.4° F.) by regulating the amount of perspira- 

 tion excreted. The amount of perspiration is influenced 

 both by the temperature of the body and of the air. The 

 evaporation of perspiration keeps the body at the normal 

 temperature. 



SUMMARY 



Man has a skeleton covered by muscles and skin. The 

 bones grow and are fed just like the muscles. This is 

 proved when the broken bone heals. The muscles are 

 the flesh covered by the skin. The muscles are both 

 voluntary and involuntary. The skin is made up of 



Dermis 



Nulnlive 

 paoilla 



Sweai &land 

 Nerve 



ood vessels 



Figure 205. — Diagram of Skin. 



