TBREE PLATES Communications between the portal and systemic venous systems have been noted in many adult forms but have never been accounted for upon an embryological basis. Krause' mentions several communications between the portal and systemic systems in the adult human, the only one of interest in connection with the subject of this paper being the branch which he describes as arising from the plexus around eitherthe small or large intestine and emptying either into the inferior vena cava or

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... the renal vein. In the cynocephalous primates there is, in the adult, a capillary plexus between the two leaves of the mesentery which connects the radicles of the mesenteric veins with the sex veins which are the representatives of the embryonic post-cardinals. In the bird, there is constantly present in the adult form, a coccygeo-mesenteric vein, which arises at the point of bifurcation of the caudal veins, runs parallel to the rectum, from which it receives tributaries, and empties into the portal vein (Parker and Haswell) .2 In an adult cat, a hitherto undescribed connection between the portal and systemic systems of veins was found. In this animal at the point of junction of the sex vein with the inferior vena cma (which, in the post-renal segment, was formed by the embryonic left post-cardinal vein as shown by it,s dorsal relation to