244 ANATOMY IN A NUTSHELL. 



surround the auriculo-ventricular openings and the arterial openings, giving 

 attachment: to the muscle fibers, valves, and great vessels. 



The endocardium is a smooth, thin membrane which lines the heart and is 

 more opaque on the left side and is thickest in the auricles, being thicker in the 

 left auricle than in the right, 



Blood Supply. — The arteries are the right and left coronary. The right 

 coronary artery arises from the anterior sinus of valsalva and passes forward 

 between the pulmonary artery and the auricular appendix. From this point it 

 runs in the right auriculo-ventricular groove to the posterior interventricular 

 groove, and here it divides into a transverse branch which runs in the left auricu- 

 lo-ventricular groove and a descending branch which runs in the posterior 

 interventricular groove to the apex of the heart. A marginal branch which 

 comes from this artery runs along the margin of the right ventricle. It also 

 gives infundibular branches to the right auricle and right ventricle and the pul- 

 monary artery. (Plate CXXVIII.) 



The left coronary artery, which is larger than the right, arises from the left 

 posterior sinus of valsalva and passes forward between the pulmonary artery 

 and the left auricular appendix. At this point it divides into a transverse 

 branch, which runs outward in the left auriculo-ventricular groove and a de- 

 scending branch which runs to the apex of the heart in the anterior interven- 

 tricular groove. The coronary arteries may come from a common trunk and 

 there may be one or two small additional branches. (Plate CXXVII.) 



The cardiac veins return the blood from the substance of the heart into the 

 righl auricle. 



1. The anterior cardiac vein, also called great cardiac vein, ascends from 

 the apex of the heart to the base of the ventricle in the anterior interventri- 

 cular groove. It turns to the left into the left auriculo-ventricular groove and 

 opens at the back of the heart into the great coronary sinus where it has two 

 valves, it drains both ventricles (more the left than the right), and the left 

 auricle. 



2. The middle cardiac vein ends in the great coronary sinus after running 

 from the apex of the heart to its base in the posterior interventricular groove. 



It has one valve at its orifice and it drains the posterior part of both ventri- 

 cles. 



:;. The posterior surface of the left ventricle is drained by the left or pos- 

 terior cardiac veins which empty into the great coronary sinus. 



1. The right or anterior cardiac veins receive the blood from the anterior 

 surface of the right ventricle and open separately into the lower part of the 

 righl auricle. The largest one of these veins, which runs along the right border 

 of the heart, is called the vein of Galen. 



5. The right or small coronary sinus drains the back part of the right 

 auricle and right ventricle and it runs in the right auriculo-ventricular groove 

 and end- in the righl end of the gr< at coronary sinus. 



('). The left or great coronary sinus is then a portion of the great cardiac 

 vein which is about an inch long and occupies the posterior part of the left auri- 

 culo-ventricular groove. It receives the veins just mentioned and also an 



