CHAPTER XIV. 



THE ANATOMY OF THE HEART AND BLOOD- 

 VESSELS. 



General Statement. During life the blood is kept flow- 

 ing with great rapidity through all parts of the Body (ex- 

 cept the few non-vascular tissues already mentioned) in 

 definite paths prescribed for it by the heart and blood- 

 vessels. These paths, which under normal circumstances 

 it never leaves, constitute a continuous 

 set of closed tubes (Fig. 76) beginning 

 at and ending again in the heart, and 

 simple only close to that organ/ Else-" 

 where it is greatly branched, the most 

 numerous and finest branches (I and a) 

 being the capillaries. The' heart is 

 essentially a bag with muscular walls, 

 internally divided into four chambers 

 (d, a, e, /). Those at one end (d and e) 

 receive blood from vessels opening into 

 them and known as the veins. From 

 there the blood passes on to the remain- 

 ing chambers (g and/) which have very 

 powerful walls and, forcibly contract- 

 ing, drive the blood out into vessels 

 (i and b) which communicate with 

 them and are known as the arteries. 

 The big arteries divide into smaller; 

 these into smaller again (Fig. 77) until the branches be- 

 come too small to be traced by the unaided eye, and these 

 smallest branches end in the capillaries, through which the 

 blood flows and enters the commencements of the veins; 



FIG. 76. The heart 

 and blood-vessels dia- 

 grammatically r e p r e- 

 sented. 



