THE CIRCULATION 



61 



opening thus made until it is large enough to slip the heart out through 

 it. Then slide back the pericardium until its connection with the large 

 blood vessels above the heart is found. 

 Observe that a thin layer of it continues 

 down from this attachment, forming the 

 outer covering of the heart. 



3. Trace out for a short distance 

 and study the veins and arteries con- 

 nected with the heart. The arteries 

 are to be distinguished by their thick 

 walls. The heart may now be severed 

 from the lungs by cutting the large 

 blood vessels, care being taken to leave 

 a considerable length of each one 

 attached to the heart. 



4. Observe the outside of the heart. 

 The thick, lower portion contains the 

 cavities called "ventricles ; the thin, 

 upper, ear-shaped portions are the auri- 

 cles. The thicker and denser side lies 

 toward the left of the animal's body and 



is called the left side of the heart ; the other is the right side. Locate 

 the right auricle and the right ventricle ; the left auricle and the left 

 ventricle. 



5. Lay the heart on the table with the front side up and the apex 

 pointing from the operator. This places the left side of the heart to 

 his left and the right side to his right. Notice the groove between the 

 ventricles, called the inter-ventricular groove. Make an incision half an 

 inch to the right of this groove and cut toward the base of the heart 

 until the pulmonary artery is laid open. Then, following within half an 

 inch of the groove, cut down and around the right side of the heart. 

 The wall of the right ventricle may now be raised and the cavity ex- 

 posed. Observe the extent of the cavity, its shape, its lining, its 

 columns of muscles, its half columns of muscles, its tendons (chordae 

 tendineae), the tricuspid valve from the under side, etc. Also notice the 

 valve at the beginning of the pulmonary artery (the right semilunar) 

 and the sinuses, or depressions, in the artery immediately behind its 

 divisions. 



6 Now cut through the middle of the loosened ventricular wall from 

 the apex to the middle of the right auricle, laying it open for observa- 



FIG. 24. Model for demon- 

 strating the heart. 



