THE SINO-VENTRICULAR SYSTEM 159 



enlargement but it really is just a change from a narrow cylin- 

 drical to a flat broad form, the absolute size remaining the same 

 in both cases and after the turn is made the branch assumes its 

 original form. 



One noteworthy feature concerning the distribution of the 

 system within the conus is found in the manner in which the 

 network terminates in the region of the pulmonary orifice. About 

 three fourths of a centimeter below the fibrous ring of the orifice 

 the injection suddenly stops around the entire circumference 

 of the conus, thus forming a uniform boundary or limitation of 

 the network. No reason could be ascertained why the termina- 

 tion should be in such uniform manner. It was found to be con- 

 stant in all hearts injected. An investigation of the musculature 

 failed to show any superficial intersection of fibres at this point 

 or any other characteristics which might be responsible for this 

 peculiar ending (fig. 5). 



As in the case of the left ventricle the most satisfactory method 

 of injecting the systems in the right is from the terminal net- 

 work (Purkinje fibres) up towards the main branch. The net- 

 work on the ventricular walls was easily filled and the injection 

 mass then forced upward along the jight crus and thence into the 

 atrium. As mentioned above the right crus is somewhat em- 

 bedded in the myocardium so that it is difficult to locate it until 

 it has been filled with injection fluid. This is another good reason 

 for starting the injection at a more superficial and lower lever 

 rather than from the right crus. 



While injecting the right crus from below it was found that 

 the fluid which had proceeded upward as far as the bifurcation 

 of the right and left crura from the crus commune passed over 

 into the left crus and followed it into the left ventricle. In 

 attempts to inject the artrio-ventricular node (Knoten) only a 

 small amount of the fluid would pass into it, because of the ten- 

 dency of the greater amount to follow the less resistant path down 

 the left branch into the left ventricle. In order to eliminate this 

 diflSculty and get more fluid into the Knoten, the following pro- 

 cedure was followed. The right crus was tied or clamped off" 

 below the point of injection and the left crus treated in a similar 



