Arterial Anomalies 43 
One artery: Fantoni (1699), Thebesius (1716), Mayer (1827), Otto 
(1830), Hyrtl (1841), Hyrtl (1855), Heitz (1901). 
2. Other Arteries from the Ascending Aorta—Bremer (1912) 
has shown that the ventral aorta is developed from a plexus 
and it seems probable that it is through the persistence of some 
of these early channels in connection with the aorta that such 
anomalies as the following are to be explained. That they are so 
very rare may be accounted for on the ground that this plexus is 
a very early formation, and is in a center of great growth activity 
and shifting of parts; any minor channels which might persist 
after the ventral aortae were established would almost certainly 
atrophy through pressure and lack of definite area to supply. 
Thymic vessels springing from the ascending aorta have been 
reported by Haller (1747), Breschet (1826) and Hyrtl (1841). 
Twice the internal mammary dextra has been observed arising 
from the ascending aorta. Such an anomaly is more difficult to 
reconcile with the above explanation unless we assume that the 
aberrant vessel of the plexus communicates with a segmental be- 
low the definitive subclavian, which in turn gives rise to the in- 
ternal mammary; such a conclusion is not warranted by any de- 
velopmental history of the internal mammary or any of its anom- 
alies with which I am acquainted. The cases are reported by 
Bohmer (1741) and Meckel (1816). 
B. Number of Branches from the Aortic Arch Less than Normal 
1. One branch from the arch. 
2. Two branches from the arch. 
1. In these cases one branch springs from the arch of the aorta; 
see fig. 37. This condition is common in some of the lower mam- 
mals; the single branch divides into brachial and cephalic trunks 
which are arranged normally. The cases of this irregularity are 
not all exactly similar ; in some the arch is apparently lacking and 
the descending aorta seems to curve over the bronchus from a 
junction with the ascending stem from its proximal portion; in 
other cases a stem springs from the top of the arch and almost 
immediately divides into the regular branches, suggesting that 
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