264 FRANKLIN P. MALL 



of these bands is then extended around the heart to the posterior 

 side much as is shown in fig. 8. As the aorta has been taken out 

 (or macerated out in MacCallum's specimens) the first break 

 into the cavity of the ventricle is immediately under the aorta, 

 in fig. 8 which is also shown in fig. 18. Here it is clearly seen 

 that the anterior papillary muscle is attached to the tip of the 

 scroll as shown in fig. 17. That this split is natural and is easily 

 made is shown by fig. 16, in which the two papillary muscles are 

 shown with a strand of muscle tissue between them. This 

 strand extends to the tip of the scroll and ends in the posterior 

 ligament of the aorta (fig. 17, PL). This figure also shows the 

 entire left ventricle unrolled with the two spiral strands hanging 

 loosely below. The one associated with the posterior papillary 

 muscle coming from the aorta is the bulbo-spiral band and the 

 other which is attached to the anterior papillary muscle is the 

 sino-spiral. Fig. 18 is made from the specimen shown in fig. 17, 

 by cutting it in half and replacing the distal end within the prox- 

 imal. In general it represents the left ventricle cut open from 

 behind, and expresses clearly the course of the break when the 

 wall of the left ventricle is unrolled. 



What is here given only apparently contradicts what Krehl 

 found when he isolated the Triebwerk of the left ventricle. My 

 illustrations (figs. 10 and 11) show that this may also be unrolled 

 if its point of origin is detached from the aortic septum. In so 

 doing the entire circular bands which pass the septum, including 

 the anterior papillary muscle, hold together, as shown in fig. 18. 

 So Krehl's Triebwerk is not composed of muscle bundles which 

 form complete rings but bundles which both arise and end in 

 the tendinous structures at the base of the heart. In so doing 

 the bundles turn upon themselves to form V-shaped loops just 

 as do the bulbo-spiral and sino-spiral bundles as they enter the 

 vortex. MacCallum's scroll again shows that all of the muscle 

 fibers form V-shaped bundles which encircle the left ventricle. 

 They are fitted into one another, those forming the circular bands 

 making obtuse angles while the outer and inner bundles form 

 acute angles at the apex. Between these two systems there 

 are all intermediate gradations. (See Schema A.) 



