38 HENRY A. MURRAY, JR. 



SUMMARY 



The processes in the early development of the rabbit's heart 

 are fundamentally the same as in the cat. 1) The primary loop 

 is due to the deepening of the left bulboventricular cleft and a 

 disappearance of the right, accompanied by a reduction on the 

 part of the right shoulder of the ventricle and a very marked 

 growth of the left. 2) The middle cardiac plate, marked tem- 

 porarily after myocardial fusion by a distinct ridge which corre- 

 sponds precisely to the line of fusion of the endothelial tubes, 

 eventually becomes entirely obliterated. 3) The primitive inter- 

 ventricular septum arises de novo from the floor of the loop in 

 a sagittal plane. 4) The left bulboventricular cleft, at first 

 horizontal, becomes oblique and then vertical; protruding into 

 the common ventricular cavity as a well-marked ridge, it meets 

 the septum developing in the apical portion of the heart and 

 contributes to the formation of the interventricular septum of 

 the adult. 



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