THE SINO-VENTRICULAR SYSTEM 157 



of a more oval and at times cylindrical shape, across the trabecu- 

 lar bridges connecting the septal and posterior ventricular walls. 



The false trabeculae are numerous in the left ventricle and 

 are found to be both short and long and of varying diameter. 

 They have been thoroughly described in the human heart by 

 Monckeberg and Tawara, and DeWitt has also examined them 

 microscopically in the beef hearts. DeWitt speaks of them as 

 the pseudotendinous threads and found all of them to contain 

 fasciculi of the S.V.S. with the exception of three or four fine 

 threads which pass from the upper part of the septal wall across 

 to their insertion in the apices of the papillary muscles. In her 

 descriptions DeWitt follows the general scheme of Monckeberg 

 of dividing the threads into the following three classes. A, 

 Threads having no cardiac muscle fibres at all but consisting of 

 connective tissue only (wirkliche abnorme Sehnenf iiden) . 

 Threads of this class were very scarce for only three or four 

 existed in the left ventricle. B, Threads carrying both myocar- 

 dial fibres and fibres of the S.V.B. The majority of the threads 

 were found to fall under this head. C, Threads carrying only 

 fibres of the S.V.B. with their connective tissue sheaths. Only 

 two small threads were found in this class. 



Particular attention was paid to the course of the injection 

 mass to see if it passed through all these classes of fibres. In 

 all cases it was seen to pass through the threads surrounding even 

 the very finest, described by DeWitt. Subsequent histological 

 examination in many cases confirmed the observed fact. The 

 anastomoses of the fasciculi of the S.V.S. are especially pro- 

 nounced within the terminal networks. Indeed, the only place 

 where individual fasciculi could be dissected out for any dis- 

 tance was in the right and left branches. As shown in figure 6, a 

 fasciculus was dissected out on either side of the left branch for 

 a distance of one and a half centimeters. 



The distribution of the right branch within the right ventricle 

 is quite as complete as that found in the left. The manner of 

 distribution is somewhat different however. The right branch 

 passes down the right side of the septum to the septal attach- 

 ment of the moderator band along which it passes to the base 



