THE SHEATH OF THE BUNDLE OF HIS 63 



A detailed description of the coursing of the finer branches as 

 shown in fig. 1 is unnecessary, but a short summary seems justi- 

 fied. On the septal wall the fibers unite, branch and reunite 

 to form a network, the meshes of which constantly grow smaller 

 until in the apex of the heart a mantle of fine anastomosing fibers 

 occurs. This lies at a region under 5 and is not well shown in the 

 figure. Upon the outer wall of the ventricle, the injected mesh- 

 work extends from the apex almost to the attachment of the leaf- 

 let of the mitral valve. Here, the fasciculi appear relatively 

 smaller, unite at more frequent intervals than those upon the 

 septal wall, and form a finer network. Moreover, the points of 

 union are more characteristically node-like. Often, fine fasciculi, 

 unnoticed before injection, became apparent and could be seen 

 to branch and to unite with others until they were finally lost to 

 view because the sheath was uninfected. 



With the sheath system in the right ventricle similar results were 

 obtained. The fluid ran down in the sheath of the right branch 

 and passed to the outer wall of the chamber by way of the mod- 

 erator band, where anastomoses occurred between the branches, 

 as in case of the left ventricle. From the outer wall other 

 strands travelled back to form a septal network. The right divi- 

 sion, however, appeared somewhat harder to inject than the other, 

 possibly because of a closer attachment of the sheath. Upwards, 

 at the beginning of the interventricular septum, it was found that 

 the injection had not extended to include the main branch. This, 

 also, may have resulted from a too firm union between sheath and 

 bundle, or perhaps from the use of too little pressure. Dissec- 

 tion of beef heart no. 37, the next in the series, showed that the 

 sheath of the main bundle had been filled with fluid as far as the 

 interauricular region — the ' Knoten' — and other specimens showed 

 the same condition. 



In the heart of the young lamb only the left side of the system 

 was injected. Here, too, a very fine and delicate system of anas- 

 tomosing fasciculi, similar in all respects to those in the larger 

 beef hearts, was brought into view. With the formalin-preserved 

 hearts of beef and calf, a like result was obtained but the extent to 

 which the fluid would penetrate within the sheaths of these was 



