138 Practical Zoology. 



experiment. Hold the heart in the left hand, with the ventral 

 surface in the palm, and the tips of the fingers against the 

 right ventricle. Hold the heart under a faucet, or pour from a 

 pitcher, and let the water run first gently, then strongly, through 

 the right auricle into the right ventricle. Watch the tricuspid 

 valves as they float up and separate the auricle from the ven- 

 tricle. Empty the heart and fill it again, and as soon as the 

 valves rise, press with the fingers on the outside of the ventricle. 

 What effect has this pressure ? Let the nozzle of the faucet 

 project down between the valves, and again turn on the water. 

 Where does the water escape ? 



4. Empty the heart and examine the valves. They will be 

 found lying close against the walls of the ventricle. Note the 

 white tendinous cords attached to the valves. 



5. Push the finger past these valves to the very bottom of 

 the ventricle ; from the outside cut through the wall of the ventri- 

 cle at this point, and cautiously cut upward in both directions 

 along the border of the ventricle. Raise the outer wall of the 

 ventricle, and study the valves more thoroughly ; with the scalpel 

 handle raise them from the walls of the ventricle. How many 

 flaps are there ? How are they arranged ? The conical eleva- 

 tions of the muscle to which the tendinous cords 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 pocketlike 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? 



