Superficial Veins in the Pig. 449 



the body wall. This receives some small veins and finally sinks 

 into the dei:)th under the anterior limb bud, receives two or three 

 twigs from it, and uniting with the anterior cardinal (Vca) enters 

 the sinus reunions in a graceful, sweeping curve. The sinus re- 

 unions also receives a vein, the inferior jugular, formed by the 

 union of a number of capillaries which rise in gill arches, where 

 they anastomose with twigs to the anterior cardinal. The veins that 

 form the anterior cardinal (Vca) are very large and striking, par- 

 ticularly the one which curves in a half circle above the anastomosing 

 tips of the cervical segmental arteries to enter the anterior cardinal. 

 A chain of anastomoses along the spinal cord, formed from the tips 

 of the segmental arteries passes from the region of the head to a 

 point below the anterior limb bud. This plexus drains back into 

 the posterior cardinal vein through its segmentals. The aorta is 

 enormous. Three aortic arches are showii. The most anterior of 

 which is not well injected. The omphalomescntpric artery (Aom) 

 is represented by four vessels which unite at some little distance from 

 their origin. In the tail the aorta divides into two vessels which 

 anastomose at the tip. 



The next embryo, Fig. 3, is a very little larger than that just 

 described, the chief point of difference being the presence of a 

 thick capillary mesh in the membrana reunions. 



As before, there remains 'a superficial part of the umbilical vein 

 (Vud) draining the posterior limb bud, which also drains largely 

 into the posterior cardinal vein. The limb bud contains a fine plexus 

 of veins which tend to form a border vein, while dorsal to it the well- 

 developed mesh runs out upon the body wall to unite with the gen- 

 eral plexus of the membrana reunions. The plexus of the mem- 

 brana reunions is evidently the same as that described by Coste. 

 It is very characteristic of the membrana, being made up of com- 

 paratively large vessels anastomosing among themselves, but for 

 the most part passing very directly to the umbilical ' vein which 

 they enter by parallel veins. 



The next embryo in the series. Fig. 4, shows these vessels even 

 better developed, since the membrana has progressed farther. It rep- 

 resents most completely the phase in the body wall when it drains 



