ON THE DEVELOPMENT OF THE HUMAN HEART 



FRANKLIN P. MALL 

 From the .1 natomical Laboratory of the Johns Hopkins t 'nivt rsity 



THIRTY-SEVEN FIGURES 



In my recent study 1 on the musculature of the adult human 

 heart it was necessary to refer constantly to the development of 

 this organ, and in general my description of the course of the mus- 

 cle bundles was also based upon their development. This made 

 it necessary to study numerous serial sections of embryo hearts, 

 as well as whole hearts which had been removed from the embryo 

 and dissected under the binocular microscope. 



It is my purpose now to give as accurate a description as possible 

 of several points which were obscure to me at the beginning of 

 my study, so this report is to be viewed as supplementary to the 

 excellent study by His as well as the recent one by Tandler. 

 First of all an attempt was made to study the course of the muscle 

 bundles and the formation of the vortex in the smallest hearts by 

 means of direct observation upon whole hearts, stained and 

 unstained, under the binocular microscope. This study was 

 controlled by that of serial sections of other hearts, an abundance 

 of material of both kinds being available. It soon became 

 apparent that the muscle wall of the entire heart had to be 

 included in this study, which soon showed that the critical point 

 lay in the wall of the atrial canal, that is the common canal be- 

 tween the atria and ventricles. The study led back to the study 

 of the valves at this point, an understanding of which is really 

 the key to the whole situation. This resulted in locating definitely 

 the atrio-ventricular muscle bundle (bundle of His) in all stages 

 of development. 



1 Mall, F. P., On the muscular architect ure of t he ventricles (if the human heart . 

 Amer. Jour. Anat., vol. 11, 1911. 



249 



THE AMERICAN JOURNAL OF ANATOMY, VOL. 13, NO. 3 

 JULY, 1912 



