Arterial Anomalies 33 
cases consist of a normal aortic arch giving rise to the right com- 
mon carotid, the left common carotid and the left subclavian ar- 
teries, while the right subclavian springs from the descending 
aorta on its dorso-lateral aspect opposite the second -or third 
dorsal vertebra, and passes behind the cesophagus to reach its 
normal position. 
The condition was first explained developmentally by Wood 
(1859), who recognized it as a persistence of the right dorsal 
aorta, fig. 12, represented in the proximal portion of the sub- 
clavian. The frequency of the condition is variously estimated 
as illustrated by the following: 
Name : Per cent No. Cases Observed 
@iainenGiS4A nes nets eee ees 4 212 
Weasel. (iO) Goocageuecscsauecos 8 
MINIT TUTE TAN TOO) lease leteraretets ates ekcvere ayer siees 4 
Wnomgon (i863) socoscodocccpn0cg6e 6 800 
Winorasom (CUson))  scoocotosvcacadgcsoes it 500 
Hehoucgy (1804) pasar oe eae ae 5 
Grinlerakeiy (tse) Neon Sere ase cies occa eae 8 
GOEZEHECE OOO) tenn e aan aicie ere ee 8 
PANidarelan 1 OR@NA) i tery secctavcle ye ccetste ca emrceenes 3 271 
While the first cases were all grouped together in one class 
when they were analyzed, Holzapfel (1899), it was seen that they 
are not all alike, but fall into different classes, as I have indicated 
above. These cases have been explained from the developmen- 
tal standpoint so frequently that it will not be necessary to repeat 
such explanations here; also reference to fig. 12 will make the 
point clear. It seems to me that one point should be emphasized 
in the developmental side of these anomalies; from a study of 
right aortic arch, see page 30, and comparing those anomalies 
with this one there is a strong suggestion that the important fea- 
ture of the irregularity is not the persistence of the dorsal root 
but the obliteration of the right fourth arch. In looking for the 
etiology of the condition we should seek a factor or factors act- 
ing abnormally on the arch. 
During the past year a case of this type was encountered in our 
dissecting rooms, the first in 150 bodies, which is in every way 
261 
