340 THE CIRCULATION OF THE BLOOD. [c HAP. XXVI IT. 



branching of each fibre, and the fusion of neighbouring branches. 

 A somewhat similar branching and anastomosis of the ultimate 

 muscular fibre has been observed at the surface of the tongue, an 

 organ of which the muscular structure is not unlike that of the 

 heart. 



The complicated disposition of the fibres of the heart on different 

 planes has, no doubt, the object of strengthening the walls of 

 its cavities, and insuring a uniformity and synchronousness in the 

 contraction of all its fibres. This arrangement belongs particularly 

 to the ventricles, where such a mode of action is most needed. It 

 may be best demonstrated on hearts which have been subjected to 

 long boiling. By this process the fibre is hardened, and may be 

 readily torn in the direction of its course, and thus by a little 

 careful manipulation, the connection of the fibres and bundles of 

 fibres may be unravelled. 



The ventricles are covered by a thin layer of fibres common to 

 both. These may be traced, apparently emerging from the apex 

 and spreading out over the anterior as well as the posterior surface 

 of the heart. At the apex these fibres pass in, to form a connection 

 with the fibres which form the innermost layer of the wall of each 

 ventricle ; from the same point these superficial fibres pass obliquely, 

 those of the posterior surface from right to left; those of the 

 anterior surface rather in the direction from left to right. At the 

 transverse fissure, they sink in to attach themselves to the fibrous 

 zone which separates auricles from ventricles. According to some 

 anatomists (Reid and others), many of the superficial fibres do not 

 pass beyond the anterior longitudinal fissure, but sink into and 

 become incorporated with those of the septum. 



If the fibres of the apex be traced inwards, they are found to 

 penetrate so as to form the innermost layers of the Avails of the 

 ventricle, contributing likewise to form the carneae columnse, and 

 becoming attached to the fibrous structures of the ventricle, both to 

 the chordae tendinse, and the auriculo-ventricular zone. Some of 

 these fibres serve to connect opposite walls of the heart : thus the 

 deep layer of fibres of the posterior wall of the heart, receives fibres 

 from the superficial layer of the anterior wall; and, reciprocally, the 

 superficial layer of the posterior wall contributes to the deep layer 

 of the anterior. But others of the superficial fibres are continu- 

 ous with the deep fibres of the same wall. These are the fibres 

 which, in passing from the superficial to the deep portion of the 

 wall, make a remarkable turn in figure of 8, of which the lower 

 portion is very small, as described and figured long ago by Lower. 



