The Animal Body 109 



of the body, but to assist the bones in giving pro- 

 tection to some of the more delicate structures and 

 organs. Within the body is the digestive system, which 

 receives and prepares the food for the use of the 

 millions of cells which constitute the living body. To 

 carry this prepared food to these cells is the work of the 

 circulatory system, composed of the heart and the blood- 

 vessels. The arteries carry the blood from the heart to 

 the different parts of the body, the minute capillaries 

 distribute it through the tissues, and the veins collect 

 the impure blood and carry it back to the heart. 

 Thence it passes to the lungs, where some of the 

 waste matters are removed and cast out in the exhaled 

 air. The respiratory system consists of the lungs, 

 with their infinite number of air-cells, and the pas- 

 sages leading to them — the windpipe and its branches 

 — through which pure air is taken in and impure air 

 breathed out. 



The urinary system, consisting of the kidneys and 

 bladder and the tubes connecting them, serves the pur- 

 pose of taking waste matter from the blood and excret- 

 ing it from the body. Closely associated with this 

 system is the reproductive system, which consists, in 

 the female, of the uterus, or womb, and ovaries, and 

 in the male, of the testicles, with the passages leading 

 from them. The function of this system is the re- 

 production of the species. 



Covering the outside of the body is the skin. Its func- 

 tions are to protect the body, to throw off waste ma- 

 terials in the perspiration or sweat, and to serve as an 

 organ of feeling or sensation. The nervous system con- 



