THE CHAMBERS OF THE HEART. 



697 



the ventricles are directed upward, backward, and to the right, and each is perforated 

 by two orifices. One of these in each ventricle is the auriculo-ventricular orifice, 

 while the other, in the case of the right ventricle, is the opening of the pulmonary 

 aorta, and is placed in front and a little to the left of the auriculo-ventricular orifice 

 upon the summit of a slight conical elevation of the base of the ventricle, termed 

 the conus arteriosus or infiindibuhini. The second orifice of the left ventricle is the 

 opening of the systemic aorta, and is situated in front and a little to the right of the 

 corresponding auriculo-ventricular orifice, immediately adjoining it. 



Compared with those of the auricles, the walls of both ventricles are very thick, 

 that of the left especially so, being from two and a half to three times as thick as the 

 right one. Unlike the auricles in another way, the inner surfaces of the ventricles. 



Fig. 660. 



Systemic aorta 



Superior vena 



Inferior vena cava 

 Eustachian valve 



Pectinate muscles 



Thebesian valve 

 guarding opening: 

 of coronary sinus 

 Posterior leaflet of 



tricuspid valve 



Pulmonary aorta 

 (pulmonary artery) 



Left coronary artery 



Leaflet of aortic valve 



Atiterior(aortic) 

 leaHet of mitral 

 valve 



Membranous part 

 of interventricu- 

 lar septum 



Medial leaflet of 

 tricuspid valve 



Anterior left 

 papillary 

 muscle 



Interventricular 

 septum 



Septal papillary muscles/ 



Posterior papillary muscle, cut 



Posterior portion of heart, hardened in situ and sectioned 

 parallel to posterior surface; viewed from before. 



instead of being even, are very irregular, being everywhere covered by muscular 

 ridges or columns, over and around which the endocardium is folded. These mus- 

 cular elevations are usually regarded as consisting of three varieties : ( i ) ridges 

 which are attached throughout their entire length to the wall of the ventricle, upon 

 which they stand out like bas-reliefs ; (2) columns which are attached at either 

 extremity to the wall of the ventricle, but are free from it throughout the intervening 

 portion of their length ; and (3) columns which are attached only by one extremity 

 to the ventricular wall and by their other extremity give attachment to slender ten- 

 dons, choreics tendinece, which pass to the edges of the valves guarding the auriculo- 

 ventricular orifices. To the columns, belonging to the first and second of these 

 groups the term columnce carnecz is applied, while those of the third group are known 



