Earliest Blood Vessels in Anterior Limb Buds. 



315 



ing with the duct of Cuvier, after the main vessel has established 

 connections through the liver. The reason for this persistence of 

 the old upper portion of the umbilical vein is now clear, for it still 

 furnishes an important drainage channel for the arm hud. 



Thus in pig embryos 7I/2 millimeters long this cephalic part of 

 the umbilical vein still receives some seven or eight tributaries from 



Fig. 18. 



Fig. 19. 



Fig. is. — Lateral view of pig embryo G mms. long, showing drainage of arm 

 bud into umbilical vein, x 11-2- 



Fig. 19. — Detailed view of venules draining the left anterior limb bud of the 

 pig embryo shown in Fig. IS, X 33i/ . 



the arm bud as shown in Fig. 20. The mammalian arm bud is 

 also drained by a series of venules opening into the posterior cardinal 

 vein. 



Summary of Results. 



The chief facts brought forward in the present investigation may 

 be summarized as followed: 



1. The first blood-vessels supplying the limb buds are capillaries 

 which grow from multiple irregular points of the lateral aortic wall 



