Superficial Veins in the Pig. 



455 



the capillaries on the mesial side of the muscle layer have a tendency 

 to unite and knot together to form a chain, the upper end of which 

 runs into the posterior cardinal. The artery is represented by a 

 few fine capillaries which run from the subclavian artery out under 

 the arch of the thoraco epigastric. 



V. Plexus 

 MR 



Fig. 7. — Section one-fourth of a millimeter thick of an embryo 15% mm. 

 long ; taken just below omphalomesenteric artery. 



MS, spinal cord ; Vtc, thoraco epigastric vein ; Ao, aorta ; Vv.cp, posterior 

 cardinal veins ; V. plexus MR, veins of the plexus of the membrana reuniens ; 

 A.om, omphalomesenteric artery ; Yais, left umbilical vein ; V.ud, right 

 umbilical vein ; M, mesonephros. 



From this stage on, however, the internal mammary vein and ar- 

 tery as well as the thoraco epigastric and the plexus of the superficial 

 epigastric developed rapidly. This further development is seen in 

 Fig. 8. The thoraco epigastric (Vte) and superficial epigastric 

 plexus (Ves) are now draining practically all of the dorsal side of the 

 muscle layer of the body wall which has grown considerably farther 



