Arterial Anomalies 19 
can attempt to classify them we must understand the theories 
that have been advanced accounting for their production. Ro- 
kitansky (1875) believed that if the concavity of the aortico-pul- 
monary septum be reversed the relative position of the aorta and 
pulmonary arteries would be reversed. Since the septum is mov- 
able all degrees of such deviation could occur. He described and 
figured sixteen different forms of transposition which he believed 
could occur, due to different degrees and combinations of devia- 
tion and nonunion of the aortico-pulmonary septum and the sep- 
tum interventriculare. In the light of recent work, Robertson 
(1913), there are inconsistencies in his figures which in a meas- 
ure destroy the classification. Also he considers a ventricle, even 
when furnished with a bicuspid valve, as right, so long as it occu- 
pies a position to the right of the other ventricle. This method 
of interpreting ventricles leads to some confusion which may be 
avoided if we identify the ventricles as bicuspid and tricuspid 
ventricles. 
Keith (1909) suggested that the atrophy of the bulbus cordis 
around the pulmonary artery is responsible for transposition. 
He, however, was apparently unaware of the function and de- 
velopment of the spiral valve in the dipnoan heart which carries 
the rotation two hundred and seventy degrees and would there- 
fore reverse the position of the aorta and pulmonary artery and 
accordingly vitiates his theory and spoils his diagram (Robert- 
son 1913). 
Robertson concluded from a study of the lower forms that 
“Tf 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.” Since the position of the 
great vessels is determined by the position of the proximal bulbar 
ridges and these, theoretically, may occupy any position, the aortic 
and pulmonary orifices may be found with the aorta in front of 
the pulmonary artery and rotating clock-wise at any point in an 
arc of 270 degrees, or rotating counter clock-wise at any point in 
a similar arc the pulmonary orifice may be rotated about the aorta. 
247 
