Arterial Anomalies B 
seems to have influenced the development of the heart; since, 
however, no constant relationship could be discovered between 
the heart anomalies and those of the arches, I will reserve the 
study of the heart for a future paper. All cases which might be 
considered to be the result of known pathological processes have 
been excluded. 
Arterial variation is but one of many irregularities encountered 
in the human body and in order to appreciate it fully we must 
consider the subject of variation as a whole, otherwise we may be 
inclined to think that arterial variations have a significance and 
perhaps an importance greater than any other anomalies encoun- 
tered. 
The first interest which variations had for observers, aside 
from being simple curiosities, was their bearing on the develop- 
ment of the individual and influence on the various medical and 
surgical procedures; then with the discovered resemblance to 
lower forms and the growth of embryological knowledge they as- 
sumed greater significance as one of the evidences of man’s origin 
from the same stem as the lower animals. Duval (1884) said: 
“En effet de cas deux ordres de variations les unes sont un sorte 
de pas fait vers l’avenir, c’est a dire vers les transformations 
futures; les autres sont un retour vers le passe c’est a dire vers” 
le transformations déja subir; les premieres sont des anomalies 
progressives, les seconds des anomalies regressives.” Bateson 
(1894) said: “ Variation in fact is evolution. The readiest way 
then of solving the problems of evolution is to study the facts of 
variation.” | 
That all variations should be interpreted as atavistic remi- 
niscence is undoubtedly incorrect. A great many more variations 
are found in man than in the lower animals. This has been con- 
sidered as an indication that the average type form is a compara- 
tively recent acquisition, hence instability, also instability due to 
progressive change toward a type not yet established which will 
more nearly meet the requirements of the organism. Probably 
the best way to view the question is to consider variation as be- 
longing to classes. Numerous observations establish a type, then 
by careful study we are able to classify the variations as belong- 
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