232 FRANKLIN P. MALL 



the inside. The sino-spiral bundle arises on the posterior surface 

 of the heart on the outside forms the anterior horn of the vortex 

 and ends largely on the anterior side of the heart on the inside. 

 The two horns of the vortex are constant in human hearts and 

 through them it is possible to divide all of the superficial fibers 

 into two distinct groups, for all of the fibers stream either to one 

 horn or to the other. By cutting the superficial fibers which cross 

 the posterior longitudinal sulcus it is seen that the right ventricle 

 is easily broken from the left. It is clear, by comparing figs. 2 and 

 3, that all of the fibers that encircle the right ventricle help to 

 make its vortex and then enter the anterior horn of the vortex of 

 the left ventricle. ^^ In separating the right heart from the left it is 

 well to keep the break as near to the right ventricle as possible 

 and in so doing it is soon observed that a large bundle crosses the 

 septum passing from the aorta to the median wall of the right 

 ventricle. This bundle is shown in fig. S, L R V, and is the one 

 described and pictured by MacCallum as ''a band of muscle from 

 the right ventricle ending in the left atrio-ventricular ring." Ac- 

 cording to MacCallum it must be cut in order to unroll completely 

 the left ventricular wall of the foetal pig. This bundle has also 

 been observed by MacCallum in the heart of a child and repeatedly 

 by Knower '*^ in the adult heart. No doubt it is this bundle that 

 Senac^'' described a century and a half ago and which has been iden- 

 tified repeatedly since. According to E. H. Weber"** the medial 

 wall of the right ventricle is thinner than that of the left ventricle 

 at the same point. The fibers are parallel to the long axis of the 

 heart, and immediately below them are the circular fibers of the 



*^ Although this point is brought out by MacCallum's method of dissection, 

 MacCallum did not demonstrate it because he studied the hearts of foetal pigs 

 which had been well macerated in a nitric acid and glycerine solution. This treat- 

 ment injures the delicate arrangement of the muscle bundles and only the coarser 

 bands remain. Moreover in the pig's heart the muscle bundles at the apex are 

 more intimately blended than in man, which explains why my description of the 

 apex of the human heart docs not correspond with MacCallum's. See Mac- 

 Callum's diagrams. 



^' Knower, Anatom. Record, vol. 2, p. 204. 



*^ Senac, Tratio du Coeur, Paris, 1849. 



" Weber, I.e., p. 150. 



