108 ALEXANDER S. BEGG 



The left half of the lower ring normally forms a large vessel 

 which winds around the dorsal wall of the intestine just posterior 

 to the duct of the dorsal pancreas, and then ascends to the liver. 

 The glandular mass of the dorsal pancreas, in growing forward on 

 the right side of the intestine, encounters this vein and becomes 

 molded about it. It sends ' ventral processes' forward, usually 

 on the right side of the vein, but sometimes on its medial side. 

 In the abnormal embryo there are two ventral processes of the 

 dorsal pancreas, both of which are shown in the figure. The nor- 

 mal course of the superior mesenteric vein, after being joined by 

 the vitelline vessel, would be under the duct of the dorsal pancreas 

 and upward on the medial side of these processes, and the shape 

 of the pancreas in the abnormal embryo indicates that such a 

 vessel was present at an earlier stage. It has, however, disap- 

 peared and the left half of the lower peri-intestinal ring, together 

 with the dorsal anastomosis of the vitelline veins, is represented 

 by a slender vessel which passes under the dorsal pancreas near 

 its distal extremity. There it is joined by the splenic vein. Be- 

 fore the left limb of the lower ring receives the splenic vein, it 

 presents a small branch directed toward another short branch 

 across the top of the pancreas. These vessels may formerly have 

 connected with one another. The unusual course of these rep- 

 resentatives of the dorsal anastomosis of the vitelline veins may 

 be explained by the plexiform nature of the original connection. 

 The upper peri-intestinal ring has developed normally. Its left 

 half has disappeared, and its right half persists as the portal 

 vein. 



Finally it should be noted that the ventral pancreas in this 

 embryo is bi-lobed, and that it bifurcates over the upper edge of 

 the abnormal vein. If its lobes correspond with those usually 

 found (cf. Lewis, '11) it is evident that the entire ventral pancreas 

 has been displaced to the right, since the ventral process of the 

 dorsal pancreas approaches its left lobe. Its relation to the vein 

 suggests that such a displacement has occurred. 



The abnormal human embryo (11.5 mm.), which has been 

 modelled in the same way as the 10 mm. pig, is shown in fig. 4. 

 Above it, in fig. 3, a normal specimen of 10 mm. is presented for 



