MUSCULAR ARCHITECTURE OF THE HUMAN HEART 225 



of the musculature of the heart would not be fully understood 

 until the muscle bundles of the septum are included in the problem. 

 Since Weber's time the problem has shifted from the study of the 

 muscular septem to that of the membraneous septum. The 

 English anatomists have been familiar with the membranous 

 septum for some time but it was not known to anatomists gener- 

 ally until it was rediscovered in Hyrtl's laboratory.-" This mem- 

 brane marks the place at which abnormal openings between the 

 two ventricles are most likely to occur, that is, persistence of the 

 interventricular foramen of the embryo. However, for a proper 

 understanding of the membranous septum it must be extended 

 to include the aortic septum. 



That the muscle bundles of the conus form relatively simple 

 riugs which attach themselves to the root of the aorta has been 

 long known. In fact, they arise and end in a raphe or tendon at 

 the point of juncture of the pulmonary artery and the aorta, as is 

 well shown in figs. 3, 8 and 13." When the conus is carefully 

 separated from the aorta in a heart which has been boiled for 

 several hours in dilute acetic acid or in a heart (preserved in car- 

 bolic acid) from which the connective tissue and fat have been 

 removed, it is found that these two vessels are firmly blended 

 along this tendinous line which when followed enters the mem- 

 branous septum. By replacing the right ventricle in figs. 3 and 8 

 it is easy to see the connection between the tendon of the conus 

 and the membranous septum. It takes but little imagination to 

 realize that these two structures are derived from the aortic 

 septum of the embiyo as has been clearly pointed out by His.^^ 

 Attention may be called at this point to the muscle bundles which 

 end in the membranous septum in figs. 3 and 8. Undoubtedly 

 they belong to the atrio-ventricular bundle which passes through 

 the membranous septum, for in early stages of development this 

 bundle passes through the interventricular foramen and becomes 



^* See Hope, A treatise on diseases of the heart, 1849, p. 302; Huschka, Wiener 

 med. Wochenschrift, 1855; Reinhard, Virchow's Archiv, Bd. 12, 1857; and Virchow, 

 Ibid, Bd. 13, 1858. 



" Krehl, I.e., Fig. 1. He has also given a good description of this tendon as the 

 tendon of the conus. See also MacCallum. 



-* His, Beitrage zur Anatomie des mensch. Herzens, Leipzig, 1886, p. 8. 



