114 DEVELOPMENT OF PRIMITIVE BLOOD-VESSELS. 



CARDINAL VEINS IN THE PIG. 



It was shown in the chick that the cardinal veins begin from dorsal diver- 

 ticula of the aorta which project into the interspaces and dilate just opposite the 

 dorsal border of the nephrotome. In the line of the nephrotome these separate 

 dilatations become connected, making a common cardinal vein which, at the 

 stage of 12 somites, is opposite every interspace. I have not the corresponding 

 early stages of the cardinal veins in the pig. In my earliest stage in the pig, 

 the cardinal veins are related to the aorta and to the spinal veins, as is shown for 

 the chick in the section on plate 3, figure 2; that is, there are direct spinal arteries 

 from the aorta to the cord and spinal veins leading to the cardinal vein. At the 

 stage of plate 4, figure 3, the posterior cardinal vein is injected, extending from 

 the zone of the ninth intersegmental artery almost to the duct of Cuvier. The 

 anterior cardinal vein is not injected, but must be present in the specimen. The 

 pig embryo shown in figure 1, plate 1, gives the best view of the cardinal veins 

 in my series. In this specimen it is clear that the anterior cardinal vein joins the 

 neural plexus cephalic to the first somite, so that the vein of the first interspace 

 which was so important in the chick is like all of the rest of the intersegmental 

 veins in the pig. Opposite the first nine somites in the pig, as shown in plate 1, 

 figure 1 , the cardinal veins appear to be an accompanying vein to the aorta. Just 

 below the ninth intersegmental artery in the pig there are the lateral arteries to the 

 nephrotomes, and over all of the rest of the course of the posterior cardinal veins 

 the lateral cardinal vein must also be considered. Opposite the first nine somites 

 I have not been able to find any direct connections between the cardinal veins 

 and the aorta, such as were shown for the earlier stages in the chick. In other 

 words, the cardinal veins are well formed rather than just beginning in all of my 

 specimens. One embryo, of the same litter as the one in plate 1, figure 1, showed 

 some tiny sprouts of the anterior cardinal vein opposite the second somite extend- 

 ing toward the aorta; sections, however, did not demonstrate any connections, and 

 I could not prove that they were not the beginning of tiny veins that soon drain 

 the pharynx. 



The series of the pig embryos also does not show the origin of the duct of 

 Cuvier, but the fact that it is made up of an extensive plexus is well shown in 

 plate 1, figure 1, as well as its relation to the umbilical veins. Below the zone of 

 the ninth somite the cardinal veins will be considered with relation to the vessels 

 of the pronephros. 



NEPHRITIC VESSELS IN THE PIG. 



The nephritic tubules in the pig receive an early and characteristic blood- 

 supply. For the limit for the chick between the pronephros and the mesonephros 

 I have followed Lilly, who regards the tubules as belonging to the pronephros 

 down to the fifteenth or sixteenth somite (page 190). For the pig I have arbi- 

 trarily followed Felix's estimation for the human embryo (1912, page 762). He 

 places the limit of the pronephros at the fourteenth somite. It will be seen in 

 figure 3, plate 4, that just below the ninth intersegmental artery a series of lateral 



