258 



THE HEAET. 



the orifices, towards the apex of the heart, where they pass with an 

 abrupt twist into the interior of the left ventricle. Their general 

 direction is not vertical but oblique, especially in front (fig. 177), just 

 as if while tlie base of the organ remained fixed the apex had been 

 twisted half round in the direction of the hands of a watch. They 

 form a distinct thin superficial stratum, best marked at the back of 



Fig. 177.- 



-SuuFACE Fibres of Vkntricles of Human Heart froii the front akd 

 BELOW (Reid). 



i, bundle of fibres emerging from tbe interior of the left ventricle at the vortex a, 

 and crossing the lower part of the septum uninteiTuptedly. At d the surface fibres are 

 somewhat interrupted. 



the right ventricle, for here the direction of the fibres is quite different 

 from those immediately beneath. At the back they pass over the 

 septum without turning in : at the front they are somewhat interrupted 

 by fibres which come out from the septnm ; except towards the base 

 and apex, where they cross uninterruptedly from one ventricle to the 

 other (fig. 177). 



To trace the further course of the surface fibres it is necessary to open 

 the left ventricle. When this is done, and the endocardium cleared 

 awav. it is seen that there are here two sets of fibres with which the 

 superficial fibres become continuous. The first of these consists of 

 bundles derived mainly from the left (or anterior) set of papillary 

 muscles, which pass down to the apex of the cavity, turning as they 

 emerge in a half circle around the front of the apex to the right side 

 {fig. 178, b). They are continuous on the outside chiefly with those 

 superficial fibres which cross the lower part of the septmn in front, 

 and which, spreading out, are attached above to the posterior parts 

 of the tendinous rings at the base. The second set, on the other 

 hand, comes chiefly from the right or posterior papillary muscles, and, 



