66 RUSKIN M. LHAMON 



scopic examination showed that the injection mass was entirely 

 held within the connective tissue envelope. At points, this 

 sheath had been dissected and separated around the entire cir- 

 cumference of the fasciculus. At other points the attachments of 

 the sheath were still partly intact and limited the injection mate- 

 rial to a part of the circumference. Where the strands anasto- 

 mose, or where a side branch is given off, as Tawara has stated, 

 the connective tissue follows each part, giving it a complete 

 investment. This was well shown by studying serial sections of a 

 part of the bundle where numbers of strands go to form one large 

 branch. The India-ink, or the Prussian-blue mass made the 

 tracing of the sheath easy, for by looking backward and forward 

 in the series the anastomosis of the near-by fasciculi enveloped by 

 a continuous connective tissue covering was marked by the con- 

 tinuity of the enclosed black or blue mass. 



Fig. 4 shows a camera lucida drawing of a section of tissue from 

 beef heart no. 26, the section being cut somewhat obliquely to 

 the long axis of the cardiac muscle cells. The figure shows the 

 transition point of a Purkinje fiber into the heart muscle, the 

 fiber showing some of the India-ink injection mass within its 

 sheath. In the series from which this section was taken the fiber 

 A is found to be a branch from B, the sheaths and the enclosed 

 injection material of the two strands, therefore, are continuous. 

 The fasciculus B, traced through the cardiac tissue for a relatively 

 great distance, gives off the short fiber A which passes at once to 

 the wedge-shaped fasciculus of cardiac muscle cells E, and becomes 

 lost in the latter at the apex. As shown in the figure, the injec- 

 tion material had travelled along in the sheath-like covering of the 

 fiber A to the point where this change takes place and the sheath 

 is seen to be directly continuous with the perimysium of the heart 

 muscle. 



This mode of transition of a fiber into a group of muscle cells, 

 is apparently one of the ways in which the sino-ventricular sys- 

 tem may terminate within the myocardium of the ventricles. 

 Tawara has discussed other forms. While an inquiry into these 

 terminal mechanisms and the histology of the same, has not been 

 the special object of this investigation, nevertheless, in tracing 

 out the ramifications of injections, into the sheath, the above 



