254 FRANKLIN P. MALL 



The superficial bulbo-spiral band, arising from the conus and 

 entering through the posterior horn of the vortex, passes up the 

 septum and blends with the deep bulbo-spiral band. In some spec- 

 imens they attach themselves at once to the aorta, as shown in 

 fig. 13. In this specimen the circular bundle around the left venous 

 ostium is unusually poorly developed. In other hearts, as in figs. 

 8 and 14, practically no attachment to the aorta is made at once 

 but all of the bands encircle the ventricle again and are finally 

 attached to the posterior ligament of the aorta. This is shown in 

 figs. 8 and 10 as well as in fig. 14. From this description it follows 

 that the bulbo-spiral band distributes itself within the left ven- 

 tricle chiefly on its posterior side. That is, it arises on the anterior 

 side of the heart, externally passes once-and-a-half times around 

 the heart and ends on its posterior side internally. 



The sino-spiral bundles, arising at the ostium behind and pass- 

 ing over the right ventricle to enter the left vortex through its 

 anterior horn, are reenforced by a thick band of muscles from the 

 interior of the right ventricle and pass at once to both papillary 

 muscles of the left ventricle which seem to be composed almost 

 entirely by them. Many fibers pass the bases of these muscles 

 and extend upward to end in the anterior side of the fibrous ring 

 of the left venous ostium. In general, they line the anterior side 

 of the left ventricle and also end in both papillary muscles. '^■^ 



This brings us to the interventricular bands. They were 

 already known to Gerdy whose description of the heart muscu- 

 lature has stood the test of time. Since E. H. Weber denied 

 absolutely the existence of these bundles'^^ they were not taken 

 seriously by anatomists until they were rediscovered and well 

 described by MacCallum. 



Fig. 2 shows a strand of muscle fibers, C, passing from the 

 vortex of the right ventricle to the apex of the left ventricle where 



*8 In the pig MacCallum associated the sino-spiral bundle exclusively with the 

 anterior papillary muscles and the bulbo-spiral with the posterior papillary muscle. 

 However, this is correct only to a certain extent, for in man the posterior papillary 

 muscle is associated with both spiral bands. This arrangement is necessary in 

 order to unroll the ventricle of the pig into a sheet, as MacCallum did. 



" Weber, I.e., p. 153. 



