3fi 



CIRCULATION OF THE BLOOD. 



14. At the extremity opposite to that where we find the capil- 

 lary vessels, the arteries and veins also communicate with each 

 other, by the intervention of the cavities of the heart. 



1.5. The result of this arrangement is, that the vascular appara- 

 tus forms a complete circle in which the blood moves, constantly 

 returning to its point of departure. 



16. The circulating circle may be compared to a tree, the 

 trunk of which is doubled upon itself, so as to cause the ultimate 

 ramifications of the branches to meet the ultimate divisions 01 

 the roots ; the upper portion of the trunk and roots would rep- 

 resent the veins. 



17. In all those animals 

 which most resemble man, 

 (anatomically,) such as the 

 monkey, the dog, horse, ox, 

 &c., the heart is placed be- 

 tween the two lungs, in the 

 cavity of the chest, which 



Fig. 5. 



ac 



ac 



vsc 



as c 



a anatomists call the thorax, 



vg (Fit/. 5.) 



18. The general form of- 

 the heart is that of an inver- 

 ted cone, the apex down, 

 and a little to the left. The 

 size of the heart is very 

 nearly that of the fist of the 

 individual to whom it be- 

 longs.* 



* Explanation of Fig. 5. The Inngs of a man with the heart and great 

 vessels which arise from it, P,P. the lungs, t. the trachea which conveys 

 air to the lungs, c. the heart, od. right auricle of the heart, vd. right veri. 

 tricle of the heart, og. left auricle of the heart, vp. left ventricle of the 

 heait, ccs. and vci. superior and inferior venae cuvse, emptying into the 

 right auricle of the heart, np. pulmonary artery going from the right ven- 

 tricle to the lungs, vp. pulmonary veins, passing from the lungs to the left 

 auricle of the heart, an. the aorta, ac. carotid arteries arising from the 

 aorta, and conveying blood to the head, asc. snbclavian vein, coming from 

 the arms and emptying into the superior vena cava. 



each 



14 Have the arteries and veins any other communication with 

 lie. than by the capillary vessels? 



15. What is the result of the arrangement of the heart and blood vessel* 

 is described ? 



16. To what may we compare the circulating circle? 



17. What is the "situation of the heart ? 



18. What is the form of the heart ? What is its size? 



