Congenital Anomalies of Arteries and Veins 3 



found in lower phila Cunningham gave the name " anticipatory 

 variations " ; obviously with this explanation there can be no quar- 

 rel, for if any one doubts he need only wait and see. To sum up 

 all of the comparative work it would seem that it has furnished 

 incontrovertible evidence of the kinship of man to the lower ani- 

 mals and has been of the greatest value in establishing the morpho- 

 logical importance of various trunks and branches ; but in the case 

 of individual variations even the most enthusiastic comparative 

 anatomist has not been satisfied with the simple fact of established 

 resemblances. How they came to be so is not answered and, per- 

 haps more important, it would seem that " Ontogeny may take an 

 entirely new course, which in all probability has never appeared 

 before and yet which immediately reaches an adaptive end result." 

 Pearl (1908). 



In conjunction with comparative work a large number of sta- 

 tistical studies have been published. They have yielded little in 

 the way of explaining the factors of variation, but have furnished 

 much exact information on their range. 



It seemed for a long time that the whole question of variations 

 was one for embryological investigation alone and many anomalies 

 have been satisfactorily explained and many more only wait a fuller 

 knowledge of the history of development ; but, as this review will 

 show, the embryologist is occasionally forced to create an " aber- 

 rant vessel " to satisfy an explanation, while the more fundamental 

 problems, which are related to growth, are still unanswered. 



In 1866 Baader, and later Aeby (1872), assumed that the pri- 

 mary vascular system was a general fine capillary net. Thoma 

 (1893) presented the hypothesis that simple physical laws operating 

 on the net determined the final adult pattern. Evans (1909) 

 demonstrated that " Before there could be said to be limb arteries 

 or veins a primitive plexus of capillaries grew into the limb tissue," 

 and in the light of this, he observed, "If these processes are at 

 work everywhere . . . the development of a given artery or vein 

 to any portion of the body can not be due to miraculous pre- 

 determination, but to definite action of physical laws." If vascular 

 variations are considered from this standpoint, they become only 

 indicators of an early disturbance of definite physical laws and, 

 conceivably, any possible variation can occur. 



