2 C. W. M. Poynter 



determining percentage frequency, except in those instances where 

 I have specifically stated some other number. In presenting the 

 bibliography the same usage has been employed as in the two pre- 

 ceding studies. 



This study is intended to supplement the earlier studies, 1916 

 and 1919, and, together with them, to furnish a complete review of 

 the vascular anomalies of the human body. 



HISTORICAL 



In the long period after Galen, when almost no direct observa- 

 tions were made, there developed in the minds of anatomists a 

 conception of the vascular system as a fixed and unvarying struc- 

 ture. Then, with the return to dissections, the wide variations 

 from the accepted types attracted attention and were recorded as 

 curiosities. A little later the growing need for exact knowledge 

 by surgeons, in order to rapidly reach and ligate vessels, gave a 

 new and added impetus to the study of the vascular tree with a 

 resulting increase in the number of recorded variations. These 

 records were soon followed by attempted explanations ; Baer, 

 Young, Serres, and others showed that certain variations corre- 

 sponded to stages of development, while other investigators found 

 similar patterns in the lower animals. It is difficult to present the 

 general aspects of the subject for the last one hundred and fifty 

 years in 'a chronological order. There is almost no subject in the 

 anatomical field which has attracted so much interest ; the bibli- 

 ography includes the name of practically every anatomist of impor- 

 tance in the last four generations. 



The problems arising from the study of vascular variations have 

 furnished a stimulus for some of the best work in the fields of 

 comparative anatomy and embryology in addition to improving the 

 work of our dissecting-rooms and furnishing a better basis for 

 descriptive angiology. 



As soon as a similarity of vascular anomalies to lower form 

 patterns was recognized a discussion began on " atavistic remi- 

 niscence " and many other of the complicated problems which the 

 enunciation of the Biogenic Law brought in its wake. For those 

 variations which could not be homologized with any of the patterns 



