Veins in Pig Embryos. 467 
o 
ie. aby? Ba 
Gtom ecylye 
of Mesonephros. 
AORTA 
Fig. 2. Embryo 8 mm. No. 2302. Sagittal section. 100”. Showing the 
capillary sprouts in the caval mesentery. The veins are ruled horizontally, the 
arteries in white, the tissues dotted. Within the liver the capillaries are 
sinusoidal in character.” The capillaries of the more ventral parts of the liver 
are not drawn in. 
b) 
speak of it as the ‘‘caval mesentery.’”’ Other capillaries also grow 
into these ridges—across the front of the aortic roots from the two 
posterior cardinal veins, from the sinuses of Cuvier, and from the 
bronchial veins in the developing lungs. At this point the sym- 
metrical development ceases, and the two ridges have very dif- 
ferent histories. On the left, the stomach lies upon the ala of that 
side, but no fusion occurs, and the ridge later disappears. The 
vessels of the stomach wall and oesophagus anastomose through 
the dorsal mesentery of the oesophagus with the anterior branches 
of the subeardinals. This suggests the oesophageal collateral 
path in portal obstruction. On the right, however, the ridge 
remains, as the ‘‘caval mesentery’’—consequently the branches 
of the r. subeardinal draining it are somewhat larger than those on 
the left. This is the condition seen in Plates III and IV. 
Depicted in Plate IV are the anastomoses between this cephalad 
extension of the subeardinal and the stomach veins; and in both 
