226 FRANKLIN P. MALL 



tied up in the membranous septum as the aortic septum closes 

 the foramen. 



A clear understanding of this region of the heart was not ob- 

 tained until the subject was investigated embryologically. Then 

 the relation of the tendon of the conus became clear, and the mem- 

 branous septum received a new meaning, in the study of anomalies 

 in the understanding of the atrio-ventricula bundle, as well as of 

 the muscle bundles of the ventricles in general. This septum is in 

 the center of the heart to which important structures pass; the 

 aorta is firmly tied to it and the contracting muscle of the ventricle 

 acts towards it. 



A brief review of the history of our knowledge of the develop- 

 ment of the membranous septum is given by His.-^ In order to 

 explain an anomalous heart Lindes-^^ studied the development of 

 the chick's heart and discovered that in its separation into right 

 and left hearts the single heart tube was divided by three inde- 

 pendent septa, namely the septum of the atrium, the septum of 

 the ventricle, and the septum of the aorta. Subsequently these 

 united as is now well known. The work of Lindes was extended 

 by His in a study of the human heart and he found that the aortic 

 septum grows from above downward to reach the septum of the 

 ventricle and finally closes the interventricular foramen through 

 the formation of membranous septum. As Lindes pointed out 

 correctly, the aorta arises in the embryo from the right ventricle 

 and through the formation of the membranous septum its com- 

 munication with the right side is cut off. All this may be seen 

 easily in fig. 3 when it is recalled that the points marked X, X.' 

 were in apposition. The figures of His are needed to make this 

 point clear.31 



According to His,^- the heart muscle, which extends over the 

 bulb of the aorta in the embryo, must degenerate in part for it 

 does not extend correspondingly high in the adult. He divides the 

 septum aorticum into three parts: (1) The inter-arterial region or 



=» His, Anatomie mensch. Embryonen, Pt. 3, 1885, S. 178. 



'" Lindes, Inaug. Diss., Dorpat, 1865. 



" His, Anat. mensch. Embryonen, Figs. 101, sa; 106, sa; 111, sa; and 118, sm. 



*2 His, Beitriige, etc. 



