THE HEART AND ITS DISSECTION 



125 



on your right, and vice versa. From this stage it will be assumed that the 

 student is able to distinguish between the four cavities of the heart, viz. 

 the right and left auricles, and the right and left ventricles. 



By means of the wood skewers we may now learn the manner in which 

 the various vessels communicate with these four cavities. The arteries will 

 thus be seen to lead direct from one or other of the ventricles, while the veins 

 communicate directly with the auricles, and indirectly through these with the 

 ventricles. Care must be taken to avoid tearing or breaking any of the 

 interior structures while applying these tests. 



The great blood-vessels may now be named as follows : 



1. Largest artery, leading direct from the left ventricle, called 

 the Aorta. 



2. Two other arteries, leading direct from the right ventricle^ 

 called the Right and Left Pulmonary Arteries. 



3. Two large veins, commu- 

 nicating with the right auricle, 

 called the Inferior and the Supe- 

 rior Venae Cavae. 



4. Two veins, communicating 

 with the left auricle, called the 

 Pulmonary Veins. 



The Aorta (Gr. airo, I raise 

 up) conveys blood from the left 

 side of the heart to all farts of 

 the body. 



The Pulmonary Arteries 

 (Lat. pulmo, a lung) convey 

 blood from the right side of the 

 heart to the lungs. 



The Venae Cavae collect the blood from all parts (the superior 

 from the upper, and the inferior from the lower parts), and carry 

 it into the right cavity. 



The Pulmonary Veins collect the blood which has circulated 

 in the lungs, and convey it into the left cavity. 



It will be noticed that the auricle and ventricle of each side 

 of the heart communicate with eacn other, so that the blood which 

 has entered the auricle can pass into the corresponding ventricle. 



We must now examine the interior of the heart. For this 

 purpose proceed as follows : 



Hold the heart with its front surface toward you (see fig. 114), and make a 

 clean cut through the wall of the right ventricle, about half an inch from the 

 groove before mentioned, and extending from the top of the ventricle to the 

 apex of the heart. Now open the ventricle by pushing aside this cut wall, 

 and observe the following points in connection with its structure : 



The wall of the right ventricle is almost entirely muscular, and numerous 

 columns of flesh (columnae carneae) project from its surface. Some of these 

 stand out like pyramids, and are called the papillary muscles (Lat. paptlla t 



Fig. 117. The Semilunar Valves 

 of the Trunk of the Pulmonary 

 Arteries, the Vessel being cut 

 and laid open. 



