44 C. W. M. Poynter 
they have simply migrated to a common point of origin. I know 
of no exact explanation for this irregularity ; it is not difficult to 
account for the fusion of the left carotid with the innominate 
trunk, but if the arch is normal the anomalous position of the 
left subclavian is more difficult to explain. 
The following cases of this irregularity have been reported: 
Troussieres (1667), Garnier, Spon & Troussiéres (1729), Haller (1768) 
(Ref. Meckel 1816), Klinz (1787), Meckel (1816), Boudant (1829), Hyrtl 
(1841-59), Dubrueil (1847), Vernon (1856). 
This type of development is found in the following mammals: Anti- 
lopidae, atherura, bos, capra, cervus, dasyprocta, equus, gazella, genetta, 
rangifer, rhinoceros, tapirus. 
2. Only two branches from the arch. This condition is repre- 
sented by a number of different types of arrangement which have 
been classified as follows: 
(a) Fusion of the ventral aortic roots or migration of the left 
carotid furnishes an innominate stem with the left carotid spring- 
ing from it and the left subclavian arising from the arch, figs. 31 
and 36. The positions of the right subclavian and carotids on 
the innominate present a number of variations; the left carotid 
may arise from the base of the innominate or a trunk may con- 
tinue for some distance after the right subclavian is given off, then 
divide into the right and left carotids; for these various arrange- 
ments see Keith (1895) and Parsons (1002). These “cases are 
numerous; Quain says twenty-five times in 219 cases, which 
probably explains why the older anatomists considered the condi- 
tion normal. Vesalius figured the condition on pages 483 and 
564. 
The following list is given of references encountered during 
this study ; it is evidently in no way representative of the number 
of times this condition has been observed; Thomson’s report 
(1893) and Adachi’s figures (1914) show a frequency of over 
10 percent. I have observed the condition only twice in my dis- 
secting rooms; in both of these cases and also in the two from 
the Warren Museum, reported below, the left carotid arose from 
the innominate trunk quite near its base; see fig. 36. 
272 
