VII 



MECHANICS OF THE HEART 



183 



The external muscular layer of the myocardium is common 

 to both ventricles 

 (Figs. 50, 51, 52). 

 Its fibres take origin 

 in the fibrous ring 

 at the base of the 

 ventricle ; they de- 

 scend obliquely from 

 above downwards, 

 and after rejoining 

 the apex of the 

 heart most of them 

 form a vortex, sink- 

 ing deeper and fur- 

 nishing almost the 

 whole of the inner 

 layer of the left 

 ventricle, papillary 

 muscles, columnae 

 carneae and muscu- 

 lar fascia oi the FIG. 52. Surface tlbres of ventricles of human heart from the front 

 nVinrrlna fori and below. (Reid.) a. Vortex of apex'; i>, bundle of fibres emerg- 



ing from exterior of left ventricle at vortex a, and crossing lower 



Of the mitral I )art of septum uninterruptedly. At d the surface fibres are 

 , somewhat interrupted. 



valves, as first de- 

 scribed by Oehl. The fibres of the internal muscular layer of the 



right ventricle, on the 

 contrary, originate in 

 the upper border of the 

 interventricular sep- 

 tum, and form numer- 

 ous reticulated, almost 

 transverse, trabeculae. 

 At different heights of 

 the ventricular cavity, 

 innumerable little 

 muscle bundles and 

 tendon fibres unite the 

 septum with the walls 

 of the ventricle, while 



Fio. 53. Section across middle third of a human heart fixed Other Separate bundles 

 in diastole. Seen in perspective. (Krehl.) The cavity of o G Pf>nrl p millnrv 

 the right ventricle shows a number of trabeculae, muscle dbCeilU <*b d,iy 



muscles, to unite by 

 the chordae tendineae 

 with the tricuspid valve 

 (Fig. 53). 



In the cavity, both of the left and of the right ventricle, two 

 parts of the internal wall can be distinguished, which are termed 



bundles and tendinous filaments, which connect the walh 

 of the ventricle in every direction with the interventricular 

 septum. The cavity of the left ventricle is much simpler. 

 The figure a4so gives a clear idea of the difference in thick- 

 ness of the walls of the two ventricles. 



