28 CHARLES F. W. McCLURE AND GEORGE S. HUNTINGTON 



anastomosis at the renal level (McC. and B., Anast.Int.Subc., 

 figs. 14 and 17), makes a cranial and a caudal connection with 

 the axial veins. As the entrance of the right sex vein into the 

 cava is in the adult usually single and caudal to that of the 

 right renal vein, the more caudal of these two embryonic con- 

 nections is the one usually retained. On the left side, the 

 subcardinal (sex vein), by a cranial and a caudal connection, 

 opens directly into the intersubcardinal anastomosis, which, 

 after the loss of the left side of the renal collar (McC. and B., 

 Anast.Subc.8prc.Sin., fig. 17), becomes the proximal portion 

 of the left renal vein. The more caudal of the two embryonic 

 connections which the left subcardinal vein makes with the 

 intersubcardinal anastomosis is in the adult the one ordi- 

 narily retained. 



Figures 26 to 32, inclusive, all represent instances in which 

 the cava has been formed by the right supracardinal vein (B, 

 fig. 1) ; they also illustrate certain variant or atypical condi- 

 tions of the internal spermatic (V. spermatica interna) and 

 the renal veins. 



In figure 26 is shown an anastomosis between the sex veins 

 of opposite sides, due to the persistence in the adult cat of 

 an anastomosis present in the embryo, between the right and 

 the left subcardinal veins (Int.Subc.Anast., fig. 1). Such an 

 anastomosis between sex veins has not yet been observed in 

 adult man. This is undoubtedly due to the fact that corre- 

 sponding intersubcardinal anastomoses are not found in the 

 embryo of man (McClure and Butler, '25). 



Figures 27 to 30, inclusive, of adult man, show interesting 

 atypical conditions of the internal spermatic or sex veins. In 

 figures 27, 28, and 29, the right sex vein communicates both 

 with the cava and with the right renal vein; in figure 28, in 

 addition to the double connection on the right side, the left 

 sex vein presents also a double communication with the left 

 renal vein. All these multiple connections which the sex 

 veins present in adult man are easily explained on the basis 

 of the persistence of the corresponding multiple connections 

 found in the embryo of man (McClure and Butler, '25, figs. 



