I. FOREWORD 



The atypical condition of the vena cava posterior (inferior) 

 often found in adult man and other mammals has for several 

 decades been a matter of much interest to anatomists, and on 

 this subject there has sprung up an extensive literature. In 

 the late nineties, I began a study of this problem; and in 

 1905, Doctor Huntingto'n became associated with me in a 

 detailed investigation of the subject. The caso de>cril>ed 

 in the literature before this time, as well as those which 

 Doctor Huntington and I had separately observed, presented 

 a wide range of atypical forms which neither of us could 

 satisfactorily explain. It now appeared to us that since an 

 atypical condition in the vena cava of an adult signifies a 

 deviation in development from the typical plan, its onto- 

 genetic interpretation would be found in the detailed study of 

 the development of all embryonic vessels which had entered 

 into the formation of the venous system. Accordingly, we 

 set about making a joint investigation of the development of 

 veins in the cat, as most of the atypical conditions observed 

 by us were to be found in the variants of this animal. During 

 the course of our work we became involved in the problem 

 of the genesis of the lymphatics, and in consequence the pub- 

 lication of our joint paper on the development of the veins 

 in the cat was delayed until 1920. It is largely due to Doctor 

 Huntington 's prolonged illness, dating from about 1D1S and 

 his death in 1!)'J7, that the publication of this memoir has been 

 delayed to the present time. 



The basic material presented in this memoir is the result 

 of our joint work, accomplished before Doctor Huntington 's 

 illness. Our purpose has been to illustrate and to interpret 

 from the standpoint of their development all known atypical 

 forms of vena cava posterior. We have constructed a c<>m 

 posite ontogenetic diagram of the embryonic venous system, 

 on the basis of which we have classified under seventeen main 



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