40 C. W. M. Poynter 
nate and left common carotid spring from the ventral aorta and 
represent the circulation from the left side of the heart. The 
ductus arteriosus is patent and joins, or is continuous with, the 
descending aorta; at the angle formed by the two the left sub- 
clavian artery is given off, see fig. 15. It seems most logical to 
account for these cases as due to disturbance with the develop- 
ment of the left arch; in this respect they are closely allied to 
cases of the more numerous type of right aortic arch, II, C, 2; 
however it seems to me that probably the disturbing factor acted 
at a later period than it did on the right arches, 7%. e., after the 
normal atrophy of the right dorsal aorta had been effected. As 
already indicated these cases present a different problem of de- 
velopmental disturbance than the case of Holst, page 26. 
Greig (1852), Struthers (1875), Osler (1880). 
5. Obliteration of the dorsal root of the left fourth arch, per- 
sistence of the left pulmonary arch. This condition is evidently 
closely related to the preceding group. The innominate, left 
common carotid and left subclavian are normal, the left arch 
terminates with the left subclavian and the descending aorta is 
continuous with the left pulmonary through the ductus arteriosus. 
This condition seems to bear the same relation to II, C, 3 that the 
preceding one does to II, C, 2. The disturbing developmental 
factor acts on a limited area, the left fourth dorsal root, but this 
same localleffect is'seen in IC. 3, ll, D2 and Wl, Dah seeinie ame 
I know of only one example of this anomaly, the case of Stei- 
dele (1778). Valenti & Pisenti (1896) have reported a case 
which is suggestive of the condition although the obliteration is 
not quite complete ; probably also some of the cases of coarctation 
of the aorta, which is not considered in this paper, are examples 
of the less pronounced effect of the same developmental dis- 
turbance. 
6. Obliteration of the right third arch, persistence of the third 
right dorsal root. 
7. Obliteration of the left third arch, persistence of the third 
left dorsal root. 
Groups 6 and 7 may be considered together, since they are 
268 
