30 C. W. M. Poynter 



out clinical interest. The lesion is present in 1.7 per cent, of the 

 hearts studied in this group. 



Lediberder (1836), Wilks (i860), Fraentzel (1868), da Costa (1870), 

 Baginsky (1879), Caesar (1880), Chiari (1880), Rickards (1881), Charteris 

 (1883), Livingston (1883), Cayla (1885), Girarde (1895), Cazin (1897), 

 Hektoen (1899), case in Guys Hospital Museum. 



C. Transposition of Aorta and Pulmonary Artery 



Abnormal positions of the great vessels coming from the heart 

 has generally been discussed under the title of transposition. 

 This condition results from anomalous rotation of the aortic 

 septum. The whole subject was clarified by the wonderful work 

 of Rokitansky (1875), but more recent investigations have sim- 

 plified his classification and corrected errors which at the time 

 of his work could not be recognized. 



Greil (1903) has shown that the bulbus cordis of more primi- 

 tive forms is represented in the mammalian heart, first forming 

 part of the anterior limb and later becoming. incorporated in the 

 wall of the right ventricle and truncus arteriosus. The truncus 

 arteriosus, as shown above, becomes differentiated into the aorta 

 and pulmonary artery by the development of the septum which 

 divides its lumen. Robertson (1913) has shown that, in Lepido- 

 siren, the septum described a spiral in a clockwise direction from 

 its distal beginning of 270 degrees. In man this spiral is some- 

 what less, or about 135 degrees. Distally the septum develops 

 laterally so that the pulmonary artery is dorsal and the aorta 

 ventral in position and as they approach the heart the positions 

 are reversed. 



In situs viscerum transversus normal rotation is reversed and 

 this septum together with other structures of the thorax and 

 abdomen present a mirror picture of the normal. When the 

 condition of reversal is limited to the heart it is known as dextro- 

 cardia. Lochte (1898) suggested that the ventricular loop could 

 rotate normally or the reverse independently of the remainder of 

 the heart. Lewis (191 5) accepted this theory and by recon- 

 structing the dififerent developmental stages in reverse rotation 

 showed that such development is possible. Much experimental 



