54 Physiology. 



above description. After the heart is severed from the lungs the auri- 

 cles may be cut off; then, by pouring water into the ventricle, the 

 action of the valves between the auricles and the ventricles will be 

 seen. Pressing on the outer surface of the right ventricle will make 

 the water escape through the pulmonary artery. If this be split open, 

 the semilunar valves at its base may be found. 



The Blood Tubes connecting the Heart with Other 

 Organs. The aorta arises from the left ventricle. The 

 pulmonary artery springs from the right ventricle and 

 sends blood to the lungs. The pre-caval and the post-caval 

 veins enter the right auricle. The pulmonary veins, two 

 from each lung, enter the left auricle. (See Figs. 31 and 32.) 



The Aorta. The aorta is the largest artery in the body. 

 It arises from the base of the left ventricle and runs a 

 short distance toward the head, then it arches over and 

 runs toward the lower part of the body. The bend, above 

 the heart, is called the arch of the aorta. At the arch 

 branches are given off which supply the right and left 

 arms, and the right and left sides of the head. Beyond 

 the arch the aorta passes behind the heart and runs along 

 the backbone and passes through the diaphragm. Just 

 beyond the diaphragm it gives off branches to the liver, 

 stomach, intestine, pancreas, and spleen. ', It gives a 

 branch to each kidney, and finally divides into two large 

 branches to the lower limbs. Numerous small branches 

 are sent to other organs; in short, the "aorta supplies 

 blood to every organ of the body except the lungs. (See 

 Figs. 29, 30, and 32.) 



The Caval Veins. There are two caval veins, the pre- 

 caval and the post-caval. The pre-caval brings the dark 

 blood from the head and arms. It has four main branches, 

 one from each side of the neck, the jugular veins ; and 

 one from each arm, the subclavian veins. These four 



