DISSECTION OP THE DOG 51 



more convex, and much the sharper, and is notched where the two longitudinal 

 grooves join a little to the right of the apex. 



Dissection. — The vessels and nerves which supply the substance of the 

 heart should now be examined. In order to do this it is necessary to 

 remove the epicardium and subjacent fat from the grooves. The remains 

 of the pericardium should also be cleared away. 



The wall of the heart is supplied with blood by the two coronary arteries, 

 right and left. 



A. coronaria dextea. — The right coronary artery leaves the aorta behind 

 the right valve which guards the exit of this vessel from the left ventricle. 

 From this point it runs along the right part of the coronary sulcus to the 

 diaphragmatic surface of the heart, where it gives off a descending branch 

 (ramus descendens) which traverses the dorsal longitudinal sulcus. 



A. coronaria sinistra. — The left coronary artery is much larger than the 

 right, and leaves the aorta behind its left valve to pass backwards to the right 

 of the pulmonary artery. Its circumflex branch (ramus circumflexus) runs along 

 the coronary sulcus to the diaphragmatic surface, where it ends close to the 

 termination of the right artery. Numerous branches ramify over the surface of 

 the left ventricle, but the largest (ramus descendens) leaves the coronary artery 

 very early and follows the ventral longitudinal sulcus. Another descending 

 branch of smaller size leaves the coronary artery close to its termination, 

 and is distributed over the wall of the ventricle. 



Vv. cordis. — -An examination of the coronary sulcus on a level with the 

 pulmonary veins and the caudal vena cava will reveal a large venous trunk 

 of no great length. This is the coronary sinus (sinus coronarius) in which the 

 large vein of the heart (v. cordis major) ends. By means of the sinus the bulk 

 of the blood from the wall of the organ is transferred to the right atrium. In 

 addition, there are numerous small veins which open directly into the atrium. 



Dissection. — Now proceed to examine the interior of the heart, beginning 

 with the right atrium. In order to open this cavity most advantageously, 

 it is necessary to make two incisions. (1) Enter the knife at the termina- 

 tion of the- caudal vena cava and carry it in a straight line to the point 

 at which the cranial vena cava joins the heart. (2) From the middle of 

 the first incision carry a second to the tip of the auricle of the atrium. 



Atrium dextrum. — As an examination of the exterior of .the heart has 

 shown, each atrium is divisible into a main part intimately connected with the 

 other atrium and the ventricle of its own side, and a freer auricle (auricula cordis) . 



Like all the cavities of the heart, the interior of the right atrium is lined 

 by a smooth, glistening membrane, the endocardium ; but the wall of the auricle 

 and the right wall of the main cavity are rendered uneven by the presence of 

 reticulate muscular ridges known as the musculi pectinati. The ridges end at 



E 2 



