THE DEVELOPMENT OF THE VENA CAVA INFERIOK. 



FREDERIC T. LEWIS, A. M., M. D. 



From the Embryoloyical Laboratory^ Harvard Medical School. 



With 11 Text Figures and Two Double Colored Plates. 



In a course of lectures on the problems of embryology, Prof. C. S. 

 Minot demonstrated that the current descriptions of the embryonic 

 vena cava inferior are inadequate, if not actually erroneous. Under 

 his direction, the rabbit embryos of the Harvard Embryological Col- 

 lection have been examined in order to revise Hochstetter's work, already 

 once repeated by Zumstein. The results of this third investigation of 

 the rabbit's cava inferior justify a new description of the vein, illus- 

 trated by lithographs, a gift from the Elizabeth Thompson Science 

 Fund. 



In rabbit embryos of about ten days, the abdominal veins are abso- 

 lutely symmetrical. On either side of the intestinal canal runs an 

 omphalo-mesenteric vein, which unites with the umbilical vein from 

 the somatopleure of the corresponding side just before joining the 

 duct of Cuvier. (See Hochstetter, 93, p. 546, Fig. 1.) For reasons 

 which have not been explained this system becomes asymmetrical, and 

 normally is predominant on the right side. On the 12th day the venous 

 orifice of the heart is on the right; the right umbilical and right omphalo- 

 mesenteric veins are larger than the left;^ and the vessels on the left 

 side are forming a new channel, the ductus venosus Arantii, which con- 

 veys their blood directly across the liver to the right auricle. 



The liver develojDS from the ventral wall of the intestine by sending 

 its tubules into, and thus subdividing the omphalo-mesenteric veins. 

 This condition was noted by Hochstetter (93, p. 54G) and others, and 

 has since been fully described by Minot (00, pp. 197-202), who named 

 the small venous subdivisions " sinusoids." 



As the venous channels become predominant on the right side, the 

 liver consequently develops more rapidly there and becomes a right- 



1 Although the right umbilical vein, in the early iDart of the 13th day, is larger 

 than the left, and may be described as "colossal," the Ze/< umbilical vein is the one 

 which persists throughout embryonic life. 

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