THE SINO-VENTRICULAR SYSTEM 155 



The fasciculi of the S.V.S, are broader at their terminal 

 branches than elsewhere in their course. The main branches 

 are made up of a greater number of fasciculi of less diameter than 

 those found in the terminal network. This fact makes the termi- 

 nal network the favorite site of injection. By insertion of the 

 needle within the main branch of the bundle it often happens 

 that the point does not remain within the sheath of a single 

 fasciculus but ruptures the sheaths of three of four surrounding 

 fasciculi. Although the needle is not within the sheath of a 

 single fasciculus the injected fluid may collect for a moment at 

 the point of injection, being temporarily retained by the general 

 loose fibro-elastic envelope of the entire bundle but finally seek- 

 ing the points of least resistance the injection mass may enter 

 the ruptured sheaths and follow the fasciculi more or less exten- 

 sively through their entire distribution. Since the general sheath 

 of the S.V.S. carries the blood supply of the bundle, it often 

 happened that some of these vessels were injected as well as the 

 fascicular sheaths. Since in the case of the flattened terminal 

 fasciculi of Purkinje fibres, the needle could be inserted into each 

 individual fascicular sheath the result was a well-defined injec- 

 tion with no extravasation into the surrounding vessels or into 

 the myocardium. 



Bearing these points in mind the complete injections were 

 made by using some of the terminal branches of the system as a 

 starting point and then gradually approaching the main trunk 

 by a series of successive injections. After locating a suitable 

 point to start from it was always an easy matter to make the 

 succeeding injections since advantage could be taken of the dis- 

 tended sheaths produced by the first injection in the subsequent 

 injections. In making more than one injection it was always 

 necessary to clamp off the punctures made by the preceding 

 one in order to retain the fluid in the injected spaces, otherwise 

 the pressure from the second injection would force it out of the 

 first perforations. In many of the hearts injected for study of 

 the distribution of the S.V.S. in the left ventricle the left crus 

 and many of its terminal branches were filled with injection mass 

 from the right ventricle, i.e., the injection was made in the right 



