POSITION OF THE HEART. 455 



from the fleshy ventricular part ; and on each surface there is a and inter- 

 longitudinal sulcus, usually occupied by whitish fat along the line Ae 

 of the coronary blood vessels, over the partition between the 

 ventricles. The interventricular groove is nearer the left border of 

 the heart in front, and nearer the right border behind. 



The auricles are two, right and left, and their wall is much Auricles : 

 thinner than that of the ventricles. They are placed deeply at the position, 

 base of the heart ; and each is prolonged forwards into a small 

 tapering part known as the auricular appendix or auricle proper, and append- 

 lled from its resemblance to a dog's ear. 



The i-r ntricles reach unequal distances on the two aspects of the Ventricles: 

 heart : thus the right one forms the lower part of the thin right right, 

 border, most of the anterior and a part of the inferior surfaces ; but and left 

 the left enters alone into the apex, and constructs the left border, 

 and the greater part of the inferior surface of the heart. 



Dissection. Before opening the heart, the coronary arteries Dissect 

 (right and left) are to be dissected on the surface, with the veins yeSdsTnd 

 and small nerves that accompany them. The two arteries will be nerves, 

 found surrounded by fat on the sides of the pulmonary artery, and 

 run in the grooves on the surface of the heart, the right one being 

 directed between the pulmonary artery and the right auricular 

 appendix into the right auriculo-ventricular groove, and the left 

 one between the pulmonary artery and the left auricular appendix 

 into the left auriculo-ventricular groove. With each artery is a 

 plexus of nerves, and that of the right side is to be followed upwards 

 to the superficial cardiac plexus. 



In the groove between the left auricle and ventricle the student and coro- 

 will find the large coronary vein, which passes to the back of the DM ' S1 

 heart to empty into the dilated coronary sinus ; and the last should 

 be defined and followed to its ending in the right auricle (fig. 167). 



The CORONARY ARTERIES are the first branches of the aorta, and TWO arteries 

 supply the heart, one being distributed mainly on the right side, [ z the heart> 

 and the other on the left. 



The right artery appears on the right side of the pulmonary right coro- 

 trunk, and is directed backwards in the groove between the right " ary> 

 auricle and ventricle, giving branches upwards and downwards to 

 the walls of those chambers. Two of these are larger than the 

 rest ; one (right marninal) runs on the anterior surface of the right 

 ventricle near the free margin ; and the other (posterior inter- 

 oentricular) descends in the posterior interventricular furrow to the 

 apex of the heart. A small branch is continued to the left side of 

 the heart, lying in the hinder part of the left auriculo-ventricular 

 groove. 



The left artery passes outwards behind the pulmonary trunk to and left 

 the left side of that vessel, where it divides into two branches. Of cc 

 these, the anterior is the larger (the anterior intfroentrictdar), and 

 descends on the front of the heart in the groove between the two 

 ventricles to the apex ; while the posterior turns backwards between 

 the left auricle and ventricle, giving left marginal and posterior 



ventricular branches. The branches of the two coronarv arteries anasto- 

 moses. 



