THE HEART. 287 



that the bundles of this layer (fig. 276 c, c' , c" ', d"), after 

 their origin from the left border of the aorta and the anterior 

 half of the ostium venosum sinistrum, Fig 2 76. 



extend obliquely downwards, and to the 

 left (c), and then, before reaching the 

 apex of the heart, curve towards the pos- 

 terior wall of the ventricle (d), whence 

 they again ascend on the septum (c") 

 and the anterior wall (c'"), and are finally 

 inserted in the whole extent of the 

 venous opening, and also in the upper 

 border of the septum (c""). It is from 

 these fibres in the free wall of the ven- 

 tricle that are derived the deep layers which decussate with 

 the superficial, and on the septum afford the fibres which, on 

 the left side, run obliquely from below and behind, upwards 

 and forwards. 



On the right ventricle, there are much fewer independent 

 fibres than on the left. Most of the superficial fasciculi are 

 continued upon the left ventricle ; both the anterior, which are 

 continued over the anterior longitudinal sulcus and lost in the 

 vortex, and also many of those which, at the posterior longitu- 

 dinal sulcus, stretch from the left to the right ventricle. These 

 latter fibres, consequently, completely encircle the right ven- 

 tricle, part of them also entering the vortex, and part, in the 

 anterior longitudinal sulcus, joining the middle muscular layers 

 of the left ventricle. Independent, superficial fibres occur 

 only: 1. at the conus arteriosus, arising from the ostium 

 venosum dextrum, between the right auricle and the aorta, sur- 

 rounding the conus arteriosus, and returning thence, from the 

 left, back to their point of origin ; 2. at the apex of the right 



Fig. 276. Diagram of the left ventricle, with the septum, in order to show the 

 course of the muscular fihres. a, a', a", superficial fibres : a, on the anterior wall ; 

 a', the turning inwards of them at the vortex ; a", their passage into the posterior 

 papillary muscle. b, b', b", septal fibres of the right side : b, their course, downwards 

 and forwards ; b', their passage into the vortex and internal muscular layer of the 

 left ventricle, as well as their termination in the anterior papillary muscle, b". 

 c—c"", middle muscular layer : c, commencement at the right side of the ostium 

 venosum, and course on the anterior wall obliquely downwards and backwards ; c' 

 curvature on the septum, and course on it, e"; c"', curvature on the anterior wall, 

 and deep course in it, to the end of the ostium venosum, c"". 



