VESSELS AND NERVES OF THE HEART. 513 



deposited between this membrane and the muscular surface; 

 being distributed irregularly in various places. 



This membrane is continued from the surface of the ventricles 

 over that of the auricles. When it is dissected off from the 

 place of their junction, these surfaces appear very distinct from 

 each other. 



The proper blood-vessels of the heart appear to be arranged 

 in conformity to the general laws of the circulation, and are 

 very conspicuous on the surface. There are two arteries 

 which arise from the aorta immediately after it leaves the heart, 

 so that their orifices are covered by two of the semilunar 

 valves. One of these passes from the aorta between the pulmo- 

 nary artery and the right auricle, and continues in a circular 

 course in the groove between the right auricle and the right 

 ventricle, and sends off its principal branches to the right side 

 of the heart. 



The other artery of the heart passes between the pulmonary 

 artery and the left auricle. It divides into two branches ; one, 

 which is anterior, passes to a groove on the surface, corres- 

 ponding to the septum between the two ventricles, and con- 

 tinues on it to the apex of the heart, sending off branches in 

 its course ; another, which is posterior and circumflex, passes 

 between the left auricle and ventricle. 



The great vein of the heart opens into the under side of the 

 right auricle, as has been already mentioned : the main trunk 

 of this vein passes for some distance between the left auricle 

 and ventricle.* 



* It was asserted by Vicussens, at an early period in the last century, and 

 soon afterwards by Thebesius, a German Professor, that there were a number 

 of small orifices in the texture of the heart, which opened into the different 

 cavities on both sides of it. 



This assertion of a fact so difficult to reconcile with the general principles of 

 the circulation, was received with great hesitation : and although it was con- 

 firmed by some very respectable anatomists of the last century, it was denied 

 by others. Some of the anatomists of the present day have denied the existence 

 of these orifices, and some others have neglected them entirely. 



The subject was brought forward in the London Philosophical Transactions 

 of 1798, Part I. by a very respectable anatomist, Mr. Abernethy, who states 

 that he has often passed a coarse waxen injection from the proper arteries and 



