Siiporficinl Veins in the Pig. 443 



tionably the same as that described by F. T. Lewis in rabbit em- 

 bryos, and called by him the external mammary vein. (Amer. Jour. 

 Anat., 1906.)* 



In general we may say that the thoraco epigastric is a vessel con- 

 necting the veins of the epigastric plexus with the axillary veins. 

 This is exactly the condition of the vein in the pig embryo of 

 about 20 mm., and though in the adult we find it has undergone 

 further change, enibryologieally it must be regarded as the same 

 vessel. 



Joris, after speaking of this same stage, says, "II est done un 

 moment ou les veins umbilicales representent les seul troncs collecteurs 

 des vaisseaux parietaux, enfin, les veines parietales perdent leur 

 troncs collecteurs par I'atrophie de la partie superieure des veins 

 ombilicales, et finissent par se rattacher au systeme veineux cave." 

 There is never a time in the embryo pig in which the umbilical 

 vein drains the whole body wall, taken in a broad sense to include 

 the limb buds, but it is certainly the chief collecting vessel for 

 a considerable period. Finally the vessels emptying into it do 

 atrophy, as the blood flowing from the body wall is directed into the 

 cardinal veins. The method by which this is effected is, as I have 

 said, chiefly through the development of the thoraco epigastric 

 vein, the description of the origin, growth and permanent condition 

 of which gives the connecting links between stages in the embryo and 

 those of the adult. 



Concerning the adult condition in man, especially in the ventral 

 body wall, much has been written, and though an account of that 

 literature does not come strictly within the bounds of this paper, 

 it may be of interest to give a brief resume of it here. It deals 

 chiefly with the question whether or not the umbilical vein remains 

 patent, and the various points of communication between the portal 

 and systemic circulation. There is considerable difference of 

 opinion, due perhaps to the different methods of attack upon the 

 problem, and to the great amount of anatomical variation which 

 unquestionably must exist. 



* Since this article went to press Dr. Lewis has also adopted the term 

 thoraco epigastric. Anier. Jour. Anat., Vol. IX, No. 1, Feb., 1909. 



