246 FRANKLIN P. MALL 



fibers is not circular but in general inclines externally towards the 

 superficial fibers of the heart and internally towards those under 

 the endocardium. ^1 Within the septum they have a transverse direc- 

 tion on the outside and within they have a general upward tend- 

 ency as shown in figs. 9 and 11. It is further observed that the 

 fibers of the deep bulbo-spiral band arise at the base of the heart 

 immediately below the origin of the superficial band which passes 

 from the same point to the vortex. This is shown in fig. 10, BS, 

 and BS', which gives this band as an extension of the longitu- 

 dinal band of the right ventricle, LRV. The entire course of the 

 deep bulbo-spiral band is shown in fig. 11. The band as a whole 

 shows the fibers turning upon themselves on the apical side, 

 then becoming circular and blending with the superficial bulbo- 

 spiral band as it comes up from the septum as shown in figs. 10 and 

 11. The point of separation between these two bands marks the 

 place w^here the muscle fibers of the left ventricle are most nearly 

 circular. Within the septum, fig. 12, X, this is not the case, as here 

 the end of the superficial bulbo-spiral band passes toward the 

 root of the aorta to which it is attached. 



It is quite easy to see that Krehl's Triebwerk, as pictured in 

 his figs. 9 and 10, includes not only the deep bulbo-spiral band but 

 also many of the fibers of the superficial which enter the heart 

 through its apex. His figures show that the fibers arise evenly 

 all around the tendon of the venous ostium, a condition which I 

 can not verify. They arise only on the left side of the aorta and 

 the ostium venosum. fig. 10, and as they pass the septum are 

 entirely free from tendinous connections with the base of the heart 

 as fig. 11 shows. In fact this separation from the base is well 

 marked in the embryo and can easily be seen in serial sections. 



As figs. 8 and 9 show, the circular bands form quite a promi- 

 nence below the opening of the aorta just above the septum. This 

 prominence is much better marked in the heart of the pig and ox, 

 so much so that it is very noticeable below the right semilunar 



*' The gradual change of the course of the fibers in passing through the heart 

 wall is from longitudinal to transverse, then to longitudinal again. This is well 

 shown in Gerdy's diagram which may be seen in Todd's C'ycloi)aedia, vol. 2, fig. 

 271. See also my schema A. 



