Arterial Anomalies 15 
literation of its cardiac opening to a slender fibrous cord in the 
normal position of the artery. It seems questionable however 
whether the same factors have always been operative in produc- 
ing these two extremes; see fig. 35. 
The case of Weiss (1875) is interesting as representing atresia 
in the conus, the pulmonary valves were present and the artery 
otherwise normal. The most frequent site of obliteration is a 
narrow band completely constricting the lumen of the vessel in 
the wall of the ventricle; it may however extend for a variable 
distance on the arterial trunk. When the artery is represented by 
a fibrous cord the aorta is usually very large and by its position, 
opening over both ventricles, suggests an unequal division of the 
truncus arteriosus by an anomalously placed aortico-pulmonary 
septum rather than a degenerative process or arrest of develop- 
ment of the pulmonary artery after it has been differentiated. 
The theory that the condition is due to a foetal endocarditis is 
generally giving place to the opinion that a developmental dis- 
turbance is the causative factor. 
This anomaly is in the majority of cases coupled with defec- 
tive development of the septum ventriculare. Rauchfuss only 
knew of fourteen cases in which the septum was complete and six 
of these were his own. It is interesting to speculate on the rela- 
tion between the two conditions and I am inclined to think from 
the evidence at hand that the obliteration of the pulmonary artery 
is the primary condition and that the failure of the ventricular 
septum to close, like the persistence of the ductus arteriosus, is 
in the nature of adaptation. The pulmonary circulation is usually 
carried on through a patent ductus arteriosus but in rare instances 
this closes normally when the bronchial arteries enlarge and as- 
sume the added function, Meckel (1816). This is one of the 
most remarkable examples of structural adaptation that has been 
recorded. 
Fig. 33 isan example of the usual appearance of the anomaly 
and the following cases are illustrative of its varying degrees. 
Fleischmann (1815), Breschet (1826), Cerutti (1827), Mauran (1827), 
Lediberder (1836), Laurence (1837), Mansfeld (1843), Chevers (1846), 
Peacock (1848), Wallis (1850), Bednar (1852), Clar (1857), Marey 
243 
