LX.] HEART-VALVES. 285 



ventricle be compressed rhythmically, the fluid will rise higher and 

 higher, until it is forced out at the top of the P. A. tube, and a 

 vessel must be held to catch it. Observe that the column of fluid 

 is supported by the semilunar valves, and above the position of the 

 latter observe the three bulgings corresponding to the position of 

 the sinuses of Valsalva. 



(<".) Repeat (/>.), if desired, on the left side, tying the long tube 

 into the aorta, and the short tube into a pulmonary vein, ligaturing 

 the others. 



(d.) Cut away all -the right auricle, hold the heart in the left 

 hand, and pour in water from a jug into the tricuspid orifice. The 

 water runs into the right ventricle, and floats up the three cusps of 

 the tricuspid valve ; notice how the three segments come into apposi- 

 tion, while the upper surfaces of the valves themselves are nearly 

 horizontal. 



(e.) With a pair of forceps tear out one of the three segments of 

 the semilunar valve of the P. A. Tie a short tube into the P. A., 

 and to it attach an india rubber tube communicating with a funnel 

 supported on a retort stand. Pour water into the funnel, and 

 observe that it flows into the right ventricle, floats up, and securely 

 closes the tricuspid valve. The semilunar valves have been 

 rendered incompetent through the injury. Turn the heart any way 

 you please, there is no escape of fluid through the tricuspid valve. 



(/.) Take a funnel devoid of its stem and with its lower orifice 

 surrounded by a flange, and tie it into the aorta. Cut out the aorta 

 and its semilunar valves, leaving a considerable amount of tissue 

 round about it. Place the funnel with the excised aorta in a filter 

 stand, and pour water into the funnel ; much of it will escape 

 through the coronary arteries; ligature these. The semilunar 

 valves are quite competent, i.e., they allow no fluid to escape 

 between their segments. Hold a lighted candle under the valves, 

 and observe through the water in the funnel how they come 

 together and close the orifice ; observe also the triradiate lines, and 

 the lunules in apposition projecting vertically. 



(g.) Slit open the P. A., and observe the form and arrangement 

 of the semilunar valves. 



[T.S. Ventricles. Make a transverse section through both 

 ventricles, and compare the shape of the two cavities and the 

 relative thickness of their respective walls. 



Casts of Heart. Study two casts of the heart-ventricles (by 

 Ludwig and Hesse), (i) in diastole, and (2) in systole. 



Effect of Ligature. Ligature any large vessel attached to the 

 heart ; one feels the sensation of something giving way when the 

 ligature is tightened. Cut away the ligature, open the blood-vessel, 

 and observe the rupture of the coats produced by the ligature.] 



