54: LABORATORY EXERCISES. 



27. STUDY OF THE BEEF HEART. (Dem.) 



Materials: The best material for demonstrating the structure of 

 the heart to large classes is an ox heart. In procuring the heart 

 from the butcher make sure that the pericardium is uninjured and 

 that the blood-vessels are left as long as possible 



Cut around the pericardium just below its attachment to the 

 upper part of the heart, and lay the sac aside, so that it may again 

 be put around the heart. Attention should be called to the con- 

 nective tissue, of which the pericardium is largely composed, and to 

 its smooth, serous lining. 



Dissect away the fat from the auricles in order that their shape 

 may be demonstrated. Make careful incisions into each of the four 

 chambers in such a way that when the walls are pulled aside, the 

 following structures may be demonstrated- the openings from the 

 auricles to the ventricles, the mitral and tricuspid valves that guard 

 these openings, the semilunar valves at the mouths of the arteries, 

 and the openings from the veins into the auricles. Call attention 

 also to the relative thickness of the walls in each chamber, and to 

 the differences between arteries and veins. 



Many points can be shown more clearly if a second beef heart is 

 cut horizontally into three parts. The first cut should be made 

 through the two auricles, just above the auriculo- ventricular orifices; 

 the second should pass across the two ventricles, half-way between 

 the apex and the openings from the auricles. It is worth while to 

 make a careful dissection of the two hearts, since they can be pre- 

 served in 4$ formalin,* and so used year after year. If possible, 

 fresh sheep hearts, dissected as directed in the preceding paragraph, 

 should be supplied the students, so they can verify the facts demon- 

 strated by the teacher. 



The following outline is suggested for recording the principal 

 facts relating to the structure of the heart. 



A. Using the descriptive terms anterior and pos- 

 terior, dorsal and ventral, right and left (with 

 reference to the animal), locate the following 



* 4% formalin is prepared by diluting 1 volume of formalin with 

 10 volumes of water. 



