THE HEART BEAT. 539 



mate base and apex and at the same time to give a rotation to the 

 apex from left to right. Mall* divides these superficial fibers into 

 two groups. First, the superficial bulbo-spiral fibers (B S) which 

 arise from the conus, the left side of the aorta, and the left side of 

 the left ostium venosum, take a spiral course to the apex, where 

 they form the posterior horn of the vortex, and penetrate to the 

 interior of the left ventricle to end in the septum and along the 

 posterior side of the ventricle, making connections also with the 

 posterior papillary muscle. Some of the deeper fibers of this 

 layer encircle the lower part of the ventricle and then pass upward 

 to end at the base of the heart. The bulbospiral fibers belong 

 chiefly to the left ventricle. Second, the superficial sinospiral 



Fig. 222 Anterior surface of the heart, to show the arrangement of the superficial fibers 

 over the right ventricle: SS, Sinospiral band; BS, bulbospiral band; B, C, fibers of the bulbo- 

 TOiral system as they enter the vortex; D, E, fibers of the sinospiral band as they enter the vortex 



fibers (S $), which arise mostly on the posterior aspect of the heart 

 from the right ostium venosum, the sinus end of the embryonic 

 heart, take a spiral course to the apex over the anterior surface of 

 the right ventricle, running more transversely than the bulbo- 

 spiral group. At the vortex this system forms the anterior horn 

 of the vortex and penetrates into the interior of the left ventricle, 

 to end along the anterior side and in the papillary muscles, par- 

 ticularly the anterior papillary. Beneath these superficial layers 

 lie corresponding deep layers of the bulbospiral and sinospiral 

 systems, which have a more transverse or circular course. The 

 deep bulbospiral fibers (B S') encircle the left ventricle and end 



* Mall, "The American Journal of Anatomy," 2, 211, 1911. 



