Frank A. Stromsten 459 



to roach tlio heart. Later, the portal vein joins tlie ]iei)atie portion of 

 the left nnibilical, so that tliere is a direct cliannel from the portal to 

 the hepatic revehent vein. The right umbilical vein does not enter the 

 liver in the lizards, hnt in snakes it very early fuses with the right 

 omphalo-mesenteric vein to form a common stem and thus comes to lie 

 within the liver for a considerable distance. Another important differ- 

 ence between the snakes and lizards is found in the fact that in the 

 former there is no direct connection between the left umbilical vein and 

 the portal, as there is. as we have seen, in the lizards. In both of these 

 reptiles, however, the abdominal portion of the right umbilical vein com- 

 pletely degenerates, wliile the same portion of the left vein continues to 

 increase in size for some time although it, too, apparently degenerates 

 after birth. 



The ahdomlnal veins. — The abdominal veins are developed, as has 

 already been stated, from a pair of small vessels which extend along the 

 ventral abdominal wall and connect the umbilical veins with the post- 

 cardinals. Later they fuse in the mid-line and connect with the portal 

 vein. As soon as this latter connection is made the connection with the 

 umbilicals is lost. According to Hochstetter, the umbilical veins do not 

 enter into the formation of the abdominal veins in lizards and snakes. 



DEVELOPMENT OF THE VEINS OF KINOSTERNON PENNSYLVANICUM. 



Unless otherwise stated, the following description will be based entirely 

 on the embryos of Kinosternon pennsijlvanicuni. Owing to the rela- 

 tively advanced stage of development of the youngest embryo studied, 

 it is not possible to describe the earliest appearance of some of the veins. 

 Furthermore, no attempt will be made to trace the development of veins 

 not directly connected with one or the other of the portal systems. The 

 plan of the present paper will be to take up first a study of the anatomy 

 and development of the hepatic portal system, and then a similar study 

 of the renal portal system. It is not the purpose of the writer to give 

 at this time a detailed comparative description of the adult venous sys- 

 tem. For this reason only those veins are mentioned whose development 

 is to be more or less carefully traced. 



HEPATIC PORTAL SYSTEM. 



Veins of Adult Kinostehxon. — Fig. 1 represents the general ar- 

 rangement of the liver veins of Kinodernon pcnnsylvanicum. As shown 

 by the figure, the hepatic venous system of turtles is made up of two 

 entirelv distinct sets of veins, the revehent and the advehent veins. 



