ANOMALIES OF THE VITELLINE VEINS 109 



comparison. The smaller embryo is somewhat younger and fails 

 to show the rotation of the intestinal loop, but in regard to the 

 veins the specimens are quite comparable. In the normal em- 

 bryo the left half of the upper ring and the right half of the lower 

 ring have disappeared. In the abnormal embryo the left half 

 of the upper ring is absent, but the right half of the lower ring- 

 remains as the direct continuation of the fused vitelline veins. 

 The ventral portion of the left half of the lower ring has disap- 

 peared, but its dorsal portion remains as the continuation of the 

 superior mesenteric vein. Although this anomaly differs from 

 that in the pig in many ways, there is a striking resemblance in 

 the dorsal displacement of the mesenteric vein, which pa>sc> 

 beneath the pancreas near its extremity. The explanation of this 

 feature is not apparent. 



In the normal human embryo the duct of the dorsal pancreas 

 opens nearer the stomach than the common bile duct. The 

 distance between the two outlets, calculated from the wax recon- 

 struction, is 0.16 mm. In the abnormal embryo, however, the 

 relative position of these outlets is reversed (as already recorded 

 by Lewis) and I find that the duct of the dorsal pancreas opens 

 0.12 mm. below or caudal to the orifice of the common bile duct. 

 It is possible that the abnormal arrangement of the adjacent 

 veins led to this anomaly, but this cannot be affirmed. The small 

 and rather rudimentary ventral pancreas in the 11.5 mm. speci- 

 men extends downward and forward in close relation with the 

 left side of the abnormal vein. 



As a summary of the observations which we have recorded, a 

 diagram (fig. 5) is presented, in which the normally persistent 

 portions of the peri-intestinal rings may be compared with the 

 parts found in the pig and in man. In these figures the term por- 

 tal vein is applied to the vessel formed by the union of the superior 

 mesenteric and splenic veins, in accordance with anatomical 

 usage, and is not extended to include the vessel made by the 

 junction of the superior mesenteric and fused vitelline veins. It 

 would be interesting to find adult specimens which had passed 

 through the abnormal stages figured, but apparently such cases 

 have not been recorded. In the human embryo which we have 



