VALVES OF THE HEART. 61 



wall of the ventricle, and study the valves more thoroughly ; 

 with the scalpel handle raise them from the walls of the ven- 

 tricle. How many flaps are there ? How are they arranged ? 

 The conical elevations of the muscle to which the chordce ten- 

 dinece are attached are the Papillary Muscles. How are the 

 valves held in place ? How are they acted on, and how do 

 they act ? 



6. Find the connection between the right ventricle and 

 the pulmonary artery; pass a probe up into the pulmonary 

 artery. Cut away enough of the wall of the ventricle to show 

 the beginning of the artery. Cut off the pulmonary artery 

 just before it forks to the two lungs; slip over the faucet the 

 end of the artery connected with the heart, and turn on a 

 little water. Watch closely the base of the artery ; turn on 

 more water, and look from below at the base of the artery, to 

 see the filling of the pocket-like Semilunar Valves. Note their 

 number, shape, and arrangement. What is the effect of the 

 stream of water upon them, and what is their effect upon 

 the stream of water? 



7. Examine the left auricle, and find where the pulmonary 

 veins enter it. Cut away the lobe of the left auricle; examine 

 its inner surface, and find the openings of the pulmonary 

 veins. Hold under a faucet, and prove the action of the 

 Mitral Valve, between the left auricle and the left ventricle. 

 Insert the nozzle of the faucet between the valves, and again 

 turn on the water. Where does it escape ? Cut off the aorta 

 half an inch from its base, and repeat the last experiment 

 with the water, meanwhile closely watching the semilunar 

 valves of the aorta. 



8. Above the pockets of the semilunar valves look for the 

 openings of the Cardiac (coronary) Arteries, which supply the 

 walls of the heart. Probe them. How many are there ? 



9. Pass the handle of the scalpel between the semilunar 



