THE ANOMALOUS PERSISTENCE IN EMBRYOS OF 



PARTS OF THE PERI-INTESTINAL RINGS 



FORMED BY THE VITELLINE VEINS 



ALEXANDER S. BEGG 



Professor of Histology and Embryology in Drake University, Des Moines, Iowa 



FIVE FIGURES 



While studying the development of the pancreas, Dr. Fred- 

 eric T. Lewis found two embryos which present anomalies of 

 the intra-embryonic portion of the vitelline veins. He has 

 referred to one of these, a human embryo of 11.5 mm., in Keibel 

 and Mall's Human Embryology (German ed., p. 421); the other, 

 a pig embryo of 10 mm., has not been previously recorded. 

 These specimens, which prove to be of considerable embryological 

 interest, were placed at my disposal, and I have made a careful 

 study of them at the Harvard Medical School, in cooperation 

 with Dr. Lewis, to whom I am indebted for many valuable sug- 

 gestions. Wax reconstructions have been prepared, both of the 

 abnormal and of normal specimens, which show the course of the 

 veins and the close correlation which exists between their arrange- 

 ment and the form of the pancreas. The models have been de- 

 posited in the collection at the Harvard Embryological Labora- 

 tory, where they may be examined at any time. 



The peri-intestinal rings formed by the vitelline veins were 

 first made known by His. In a familiar figure, here reproduced 

 as fig. 1, he showed that the right and left vitelline (or omphalo- 

 mesenteric) veins anastomose with one another at three places, 

 namely (1) ventral to the intestine within the liver; (2) dorsal 

 to the intestine below the dorsal pancreas; and (3) ventral to the 

 intestine above the yolk-stalk. Thus two venous rings are pro- 

 duced, each of which encircles the intestine. He showed, more- 

 over, that the left half of the upper ring and the right half of the 



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