MALFORMATIONS OF THE BULBUS CORDIS 7 



a distinct thickening at the points indicated by 4 and 5. These 

 thickenings mark the junction of the infundibulum with the bod}^ of the 

 right ventricle, and represent the position of the lower or ventricular 

 orifice of the bulbus cordis. On the septal wall of the infundibulum are 

 seen two muscular bands or plates, the right (A) and left (B) septal 

 bands, with between them a faintly marked and rather diffuse raphe. 

 The septal wall of the infundibulum, formed by the two muscular bands 

 or plates just mentioned, is only 20 to 25 mm. in length, while the lateral 

 or marginal wall of the infundibulum is twice that depth or more. Its 

 muscular walls are dense, the fibres are in the main circular in direction ; 

 the uppermost fibres surround the base of the pulmonary valves, and, 

 as is well known, render these valves competent by their tonus in 

 diastole. The infundibulum of the right ventricle is manifestly 

 different in structure, and presumably also in function, from the body of 

 the right ventricle, and I regard it as derived directly from the bulbus 

 cordis, the muscular thickening between the two parts of the ventricle 

 representing the ventricular or lower orifice and the pulmonary opening 

 the aortic or upper orifice of the bulbus cordis. 



In studying the evolution of the mammalian from the primitive 

 four-chambered heart of the fish, one recognises that three great changes 

 have taken place; (i) the primitive auricle and ventricle have become 

 completely divided into right and left chambers ; (2) the sinus venosus 

 has become partly or, as in man, almost completely, submerged in the 

 musculature of the right auricle ; (3) the bulbus cordis has become 

 separated from the left ventricle and aorta, and completely incorporated 

 in the right ventricle as the infundibulum of that chamber. That such 

 was the fate of the bulbus cordis in the mammalian heart, I became 

 convinced four years ago from a study of the malformations and 

 comparative anatomy of the heart, but my evidence was incomplete 

 until Greil published the results of an exact and complete research into 

 the embryological history of the bulbus cordis, and demonstrated its fate 

 in the mammalian heart. (For abstract of Greil's research see Hoch- 

 stetter's account in Handbuch der Vergleick, u. Experim Entwickelimgs- 

 lehre der Wirbeltiere, parts 4, 5, 14, 15, 1903). The cavity of the bulbus 

 cordis is incorporated in the right ventricle by an upgrowth of the 

 ventricular musculature round it, the musculature of the bulbus being 

 thus replaced by the musculature of the ventricle, in the same w^ay as 



(61) 



