614 APPENDIX 



Musculi Papillares. These are muscular columns attached at 

 one end to the walls of the ventricle, and at the other to the chordce 

 tendinece. These are delicate tendinous cords which pass from 

 the musculi papillares to the edge of the valve segments. The 

 muscles and cords prevent the segments of the valve being forced 

 into the auricle by the weight of the blood behind them. 



The Tricuspid Valve. Pass the finger from the auricle into the 

 ventricle and distend the auricula-ventricular orifice. Note that 

 it is surrounded by three fibrous sheets which hang down into the 

 ventricle and are connected at the sides to the musculi papillares 

 by the chorda tendinew. This is the tricuspid valve. 



The Pulmonary Artery. With the scissors, extend the incision 

 upward through the pulmonary artery and note that the mouth of 

 the artery is surrounded by three membranous cups, the semilunar 

 valve. Each constitutes a sort of pocket, and all three together 

 when distended close the opening of the artery completely. 



Opening the Left Auricle. Make an incision in the appendix so 

 as to see the interior of the auricle. Note the two portions, the 

 appendix and the atrium. It resembles the right auricle. 



The Pulmonary Veins. Hold the heart so as to see the depth of 

 the atrium and note that it presents a ridge at right angles to it. 

 Hold the organ to the light and note the openings of the pulmonary 

 veins near the ridge. 



Opening the Left Ventricle. With the scalpel transect the left 

 ventricle, carrying the incision to the apex. The left ventricle 

 forms the apex 'of the heart. The auriculo-vbntricular opening of 

 this side is surrounded by the mitral or bicuspid valves. Note the 

 chordce tendinece and musculi papillares. 



The Aorta. Pass a probe into the aorta and follow the course 

 of the probe with the scissors, thus opening the aorta. Note the 

 semilunar valves guarding its orifice. Note the openings of other 

 blood vessels from the aorta, the coronary arteries, just above the 

 valve. Observe the smooth lining of the aorta, as well as of the 

 auricles and ventricles. 



THE CIRCULATION OF BLOOD IN THE FROG'S FOOT 



A live frog is wrapped carefully in moist cloth except one leg. 

 The projecting foot is secured on the microscope stage in such 



