230 FRANKLIN P. MALL 



It is formed largely by His' septum aorticum superius or Krehl's 

 tendon of the conus. It is shown in fig. 3, X, X', and fig. 8. 

 The muscle bundles of the conus as well as the bulbo-spiral band 

 arise from this ligament. The right ligament which is much better 

 marked in the pig and dog than in man sends a delicate lateral 

 branch around the right venous ostium to form the anterior seg- 

 ment of the right fibrous ring.*^ To sum up, the aorta is tied to 

 the heart muscle by three ligaments, as well as through the valves 

 to the papillary muscles. Two of these ligaments, the right and, 

 the posterior, are derived directly from the membranous and 

 aortic septa, while the third, the left, seems to be independent of 

 them, encircles the heart to the left, and marks the line of separa- 

 tion between the origin of the bulbo-spiral and sino-spiral muscu- 

 lar bands. 



The superficial fibers of the heart, all of which arise from the 

 tendinous structures at the base (septum aorticum and its exten- 

 sions), pass spirally towards the apex of the heart to form the 

 great vortex there. Above they form a thinner layer than below; 

 as they approach the apex the fibers must either diminish in num- 

 ber or they must form a thicker layer. Probably both conditions 

 prevail for fiber bundles are constantly leaving the superficial 

 layer to pass into the depth, but transverse sections as well as 

 dissections show that the main superficial fiber bundles gradually 

 become piled upon one another as the apex is approached until 

 they finallj^ form the whole thickness of the heart wall at this point 

 In other words there are no circular fibers in the apex. 



At the vortex all of the fibers penetrate the heart to form the 

 inner layer of the heart muscle of the left ventricle, as is well 

 known. Here they spread upward and finally are attached again 

 at the fibrous bands from which they arise. However, in general 

 a bundle which arises at a given portion of the heart on the outside 

 returns to the opposite side of the ventricle on the inside. Thus, 

 bundles arising from the septum aorticum in front of the heart on 

 the outside, the bulbo-spiral bundle, and posterior to the aorta on 



■•^ The tendinous bands just described are well illustrated in Toldt's Atlas, 

 fig. 932. 



