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ELEMENTARY PHYSIOLOGY 



We may now examine the blood-vessels at the base of the heart. If some 

 of them appear to be small, portions may be cut down till we arrive at the 

 point where the smaller vessels unite to form a large one. In this way we may 

 readily reduce the number of blood-vessels to about seven. Some of these 

 have very thick, firm, and elastic walls, which retain their circular form, 

 although the vessels are quite empty. These are the arteries, which convey 

 the blood from the heart. The other vessels have thinner walls, which are 

 comparatively inelastic and limp. These are the veins, which bring the 

 blood to the heart. 



It is now necessary to learn which is the right and which the left side of 

 the heart On the surface will be seen two grooves, on opposite sides, one 



Fig. 1 1 6. The Human Heart from behind. 



i, right ventricle ; 2, left ventricle ; 3, 3', and 3", the pulmonary arteries and their branches \ 

 4' and 4", the aorta ; 5, right auricle ; 6 is placed on the division between the right and 

 left auricles ; 7, superior vena cava ; 8, inferior vena cava ; 9, hepatic vein ; 10, u, and 12, 

 right pulmonary veins ; 13 and 14, left pulmonary veins ; +, the coronary arteries. 



situated in front and the other behind. Inside the heart, extending between 

 these grooves, is a fleshy partition which separates two cavities called the 

 ventricles (Lat. ventriculus, a little belly) the right and the left. These 

 ventricles constitute the greater part of the heart, and are much stronger and 

 more muscular (fleshy) than the auricles. We may now readily distinguish 

 between the right and the left ventricles by pressing their walls between the 

 finger and thumb, the walls of the left ventricle being much thicker than those 

 of the right. 



Now hold the heart before you in the position it would occupy (see fig. 1 15), 

 supposing it to be the heart of a person facing you : that is, with its base 

 uppermost and its apex inclined to the left (your right), the left ventricle being 



