MALFORMATIONS OF THE BULBUS CORDIS 13 



marked A and B in figures 2, 3, form here functional parts of the wall of 

 the right ventricle, which throws its contents into the aorta. This class 

 of case and the one described just before this, make up over 50 per cent. 

 of the cases usually classed under congenital pulmonary stenosis. 



In the cases dealt with so far, the bulbus has been arrested in its 

 growth and expansion after the upgrowth of the ventricular musculature, 

 but there still remains for consideration a very considerable group of 

 cases, in which the arrest of development is almost complete. In figure 

 6 a case of this kind is represented ; in that figure two views are given 

 of the heart of a girl aged two years. In A, the heart is represented 

 unopened ; the commencement of the pulmonary artery was represented 

 by a thread of tissue ; in B the right ventricle is opened, and all that is 

 seen of the infundibulum or bulbus is a slight cleft with fibrous lining 

 exposed by section of the wall of the ventricle, just in front of the aortic 

 orifice. The septal bands A and B of the infundibulum are shown 

 completely fused in the muscular wall of the ventricle, and unless one 

 knew where to look and what to look for, the remaining trace of the 

 bulbus would pass unobserved. The various conditions of the infun- 

 dibulum of the right ventricle, which I have just described, constitute by 

 far the great majority (over 90 per cent.) of the cases classed as 

 congenital pulmonary stenosis. It will be seen that the condition is 

 usually one which affects much more than the orifice of the pulmonary 

 artery ; it involves a complete segment of the right ventricle. Further, 

 the condition is not one which can be accounted for by a foetal endo- 

 corditis ; the form and extent of the lesion can only be accounted for by 

 accepting the hypothesis that the infundibulum is derived from the 

 bulbus cordis, a fusiform chamber, with a thick, endocordial lining, which 

 becomes incorporated in the right ventricle during the first month of 

 development, and whatever agent may be at work in producing this 

 malformation must exert its effect at this early stage of development. 



Having now indicated the part of the right ventricle, which is derived 

 from the bulbus cordis, and the numerous malformations to which it is 

 liable, it is necessary to explain the manner in which the bulbus cordis 

 becomes restricted to the right side of the heart. When it is remem- 

 bered that the aorta, as well as the pulmonary artery is derived directly 

 from the primitive aortic stem, it is apparent that, in the mammalian 

 heart, both of these vessels ought to spring from the part of the heart 



(67) F I 



