206 THE POCKET ANATOMY 



Valsalva. The point corresponding externally to these valves 

 is the upper border of the junction of the third left costal 

 cartilage with the sternum. 



The LEFT AURICLE consists of a principal cavity and an 

 appendix auriculae ; the latter extends forwards and to the 

 right side, projecting over the commencement of the pul- 

 monary artery. Its interior presents musculi pectinati as on 

 the right side. 



OPENINGS. The pulmonary veins (4) open into the cavity, 

 two on either side. 



The auricula-ventricular opening is smaller than that on the 

 right side. 



On the septum may be seen a shallow depression, the re- 

 mains of the foramen ovale. 



The LEFT VENTRICLE is longer and more conical than the 

 right, with its walls nearly three times as thick. The interior 

 contains columnae carneae, musculi papillares, and chordae 

 tendineae, as on the right side. 



OPENINGS. The auricula-ventricular opening corresponds to 

 the junction of 4th left costal cartilage with the sternum ; it is 

 closed by the mitral valve, which is attached to the circum- 

 ference at the opening, similarly to the tricuspid. It consists 

 of two flaps, the larger being anterior (aortic cusp). 



The aortic opening is placed in front and to the right side of 

 the preceding, and its position may be marked externally by 

 a line drawn through left half of the sternum, on a level with 

 the lower border of the 3rd left costal cartilage. The orifice 

 is guarded by three semilunar valves, which are precisely 

 similar to those on the pulmonary artery, the characteristics 

 of which are, however, better marked ; they are named from 

 their position anterior, right posterior and left posterior. 



The endocardium is the serous membrane lining the whole 

 of the interior of the heart, and is continuous with the lining 

 membrane of the bloodvessels. 



The coronary arteries supply the substance of the heart. 



The right coronary artery comes off from the anterior sinus 

 of Valsalva (aortic), passes on the right side of the pulmonary 

 artery, between it and the right appendix, then backwards 

 along the right auriculo-ventricular groove as far as the 

 posterior inter-ventricular groove, where it divides into two 

 branches, one of which passes transversely in the left auriculo- 

 ventricular groove and joins branch of left artery, whilst the 

 other passes downwards in the posterior inter-ventricular 

 groove to supply the ventricles and septum ; anas descending 

 branch of left artery 



