42 



The Semilunar Valves. From the base of the right 

 ventricle arises the pulmonary artery. Within its base, 

 just as it leaves the ventricle, are three pocket-like valves, 

 like " patch-pockets." They are in a circle, with their edges 

 touching, and thus surround the opening, with their 

 mouths opening away from the heart. A similar set of 

 valves are within the base of the aorta, which arises from 

 the left ventricle. Both these sets of valves are called 

 semilunar valves. 



Dissection of the Heart. No description (nor even figures) can 

 give a clear idea of the heart. A good model will be of some assist- 

 ance. But the heart itself should be examined carefully and then dis- 

 sected. The heart and lungs of a sheep should be obtained (ask the 

 butcher to save the "pluck," i.e. the heart and lungs taken out together). 

 The relations of the heart to the lungs and other organs should first 

 be studied, and then the pericardium opened. Observe the outside of 

 the heart, and then cut the heart open to see the points given in the 

 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 (the largest artery in the body) 

 arises from the base of the left ventricle, and supplies 

 with blood every organ of the body except the lungs. 

 The pulmonary artery springs from the base of the right 

 ventricle and sends blood to the right and left lungs. 

 Two large veins enter the right auricle, the precaval vein 

 from the anterior regions of the body and the postcaval 

 vein brings blood from all the organs of the posterior por- 

 tions of the body. The pulmonary veins return the blood 

 from the lungs to the left auricle, two from each lung. 



