THE MAMMALIAN VENA CAVA POSTERIOR 17 



VI. THE ATYPICAL FORMS OF THE VENA CAVA POSTERIOR IN 

 ADULT MAN AND THE CAT, INTERPRETED ON THE BASIS OF 

 THEIR DEVELOPMENT FROM A COMMON GROUND PLAN, BY 

 THE SELECTION OF POTENTIALLY AVAILABLE PATHWAYS IN 

 THE EMBRYO 



In the following pages there are given examples of atypical 

 forms of the vena cava posterior thus far observed in both 

 man and the cat. These atypical conditions can be inter- 

 preted on the basis of their development from a common 

 ground plan, through the selection of potentially available 

 venous pathways in the embryo. The variants described for 

 man have been drawn from the anatomical literature dealing 

 with this topic and from the extensive Huntington Collection 

 in the College of Physicians and Surgeons of Columbia Uni- 

 versity. The adult material of the cat was in large part pre- 

 pared by Professor William Darrach, in connection with the 

 courses in mammalian anatomy in Columbia University. He 

 examined 605 adult cats, and at the Twenty-first Annual 

 Meeting of the American Association of Anatomists (Decem- 

 ber, 1906), reported the variations of the vena cava posterior 

 and its tributaries, as shown by this series. His report is pub- 

 lished in the Proceedings of the Association, Anatomical Rec- 

 ord, no. 3, 1907. We wish here to express our deep obligations 

 to Professor Darrach for his painstaking work, done largely 

 in our behalf. Since the work of Professor Darrach, further 

 extensive observations have been made by the writers in the 

 Departments of Comparative Anatomy of Princeton and 

 Columbia Universities. 



As we have shown elsewhere, certain of these embryonic 

 venous pathways which are not retained in the adult undergo 

 atrophy, and the position formerly held by them is assumed 

 by a lymphatic. This process has been termed by us the 

 "extra-intimal replacement of a vein by a lymphatic." For 

 a more complete understanding of the process involved, the 

 reader is referred to our joint paper published in 1907, 5 in 

 which this view was first advanced, and to papers published 

 by us separately in 1910. 



5 Am. Jour. Anat., vol. 6 (Proc. Ass. Amor. Auat.). 



MKM01R 15 



