Congenital Anomalies of the Heart 3 1 



work has been done with the problem of reverse rotation and 

 while the subject still is obscure in many particulars, there seems 

 to be no reason why disturbing factors should not produce a 

 reversal of the ventricular loop without other heart structures 

 being influenced by them. 



The various types of transposition seem to be the result of dis- 

 turbances of normal rotation of the various parts of the heart. 

 Rokitansky (1875) believed that if the concavity of the aortic 

 septum be reversed the relation of the aorta and pulmonary 

 artery would be reversed. His extensive classification failed to 

 take into account the possible movement of the ventricular loop, 

 also he considered a ventricle, even when guarded by a bicuspid 

 valve, as right when it occupied a position on the right side of 

 the viscus. It has since been shown by Lochte and others how 

 important it is to identify the ventricle as tricusped or bicusped. 

 Keith (1909) suggested that the atrophy of the bulbus cordis 

 around the pulmonary artery is responsible for the transposition ; 

 Robertson (1913) has shown that his theory is contrary to fact, 

 for while he places the aortic orifice on the right and the pul- 

 monary on the left of the bulbus cordis, exactly the reverse is 

 true in the dipnoan heart. Robertson concludes from a study of 

 lower forms that " If the bulbus cordis develops as a short, 

 straight tube without any disparity in the length of the walls of 

 its middle segment, no torsion of the vessels, that is, the aortico- 

 pulmonary septum, will take place, the middle part of the bulbus 

 cordis where it should occur being so to speak wiped out." 



A -study of the cases seems to reveal three distinct conditions 

 which may be classified as follows (Poynter 1916) : 



1. A failure of rotation of the aortic septum in a heart in 

 which the ventricular loop has developed normally. The aorta 

 is in front of the pulmonary artery and opens from a tricusped 

 ventricle. This is the most frequent form of transposition. 



2. A failure of rotation of the aortic septum in a heart which 

 has developed by rotation in the reverse direction. The aorta is 

 in front of the pulmonary artery and opens from a tricusped 

 ventricle. The condition is the mirror picture of the previous 

 group and may be found in situs viscerum transversus. 



