Frank A. Stromsten 479 



a stout anastomosing branch from the subcardinals of the same side. 

 The portion of the postcardinal between the cranial end of the meso- 

 nephros and the sinus venosus, that is to say the az3^gos portion of 

 Lewis, 04, is broken up into two or three vessels; often one large vein 

 and one or two much smaller, all of which open separately into the ducts 

 of Cuvier. While this would seem to correspond with the condition 

 found in lizards, it is interesting to note that in Chelonia the post- 

 cardinals retain their identity as distinct vessels throughout their entire 

 course, and are not broken up cranially into broad blood sinuses as they 

 are in lizards. The conditions here met probably represent the remains 

 of the venous plexus described by Brouha in the chick. The postcar- 

 dinals are still connected with the umbilicals by a number of anasto- 

 mosing branches. 



The postcardinals already receive a series of intersegmental branches 

 from the dorsal body wall and also a number of branches from the mesen- 

 tery ventral to the aorta. As soon as the anterior limb ridge is formed, it 

 sends six or eight vessels to the postcardinal. These limb veins, as 

 Hoffmann, 90, has already shown in the lizards, comes from between the 

 successive myotomes of which the limb is developed. They also connect 

 at this time with the umbilicals. 



The name subcardinals was given by Lewis, 02, to a pair of veins 

 which extend along the ventromedial border of the mesonephroi and cor- 

 respond to the venae renales revehentes of Hochstetter. According to 

 Lewis, 02, 04, the subcardinal veins are split off from the mesonephric 

 portion of the postcardinals (" Mesonephric azygos "). Miller. 03, claims 

 that " The subcardinal veins arise in birds as unconnected vessels or 

 islands, which are without doubt independent structures; and the con- 

 nections with the postcardinals are formed later and secondarily." (Mil- 

 ler: Am. Jour. Anat., Vol. II, p. 286.) 



In a 7.4 mm. turtle embryo the subcardinal veins extend from near 

 the root of the tail forward along the ventromedial border of the meso- 

 nephroi to a point somewhat craniad of the origin of the omphalo-mesen- 

 teric artery where they open into the postcardinals. The subcardinal 

 veins do not appear to be connected with each other in any way at this 

 stage, although, on the other hand, their connection with the postcar- 

 dinals is very complete, both through direct connections and through the 

 venous network of the mesonephroi. 



Both the postcardinals and the subcardinals are still very small. The 

 mesonephroi are very simple, being scarcely more than a series of seg- 

 mentally arranged tubules opening into the mesonephric ducts. 



As the mesonephroi increase in size and complexity, the postcardinal 



