Veins in Pig Embryos. 463 
identical with the bilateral renal veins of His, and the subear- 
dinals of Lewis.) Communications were set up through the sub- 
stance of the Wolfhan body with the cardinal veins; especially the 
right; later with the kidneys, and so the ground plan of the adult 
cava was laid. For more detailed accounts of these conditions as 
given by Hochstetter, one is referred to his own articles and. to 
various anatomies and embryologies. 
In considering these points, we must not forget Zumstein, 
whose work, criticised adversely by Hochstetter, has enjoyed little 
recognition. He studied rabbit and mole, as well as human 
embryos, and while his reconstructions are diagrammatic in the 
extreme, he observed that the subcardinals exist before the vena 
cava, and communicate with the liver veins by small vessels. 
(“‘Gegen der Kopfende der Urniere treten beiderseits medial und 
ventral von den Cardinalis kleine Venenlumina aus, welche mit 
den Kardinal-Venen sich verbinden. Die rechten lassen sich 
an die Lebergefaisse heran verfolgen. Sie sind noch kapillar. 
In der Leber selbst tritt noch kein deutlicheres Gefass- 
lumen hervor, dass man als cava inferior ansprechen kénnte.”’ 
Anat. Hefte, I. 1898, 8. 311. The quotation, given also by F. T. 
Lewis, concerns an embryo mole, 3 mm. in length). As Lewis 
observes, he did not appreciate the point, and did not push it. It 
will be seen by this time that the question is almost entirely one of 
interpretation. 
It remained for F. T. Lewis (01) to describe the subcardinal 
veins as such. He saw that they antedated the cava, and that 
they approach very close to the venous spaces of the liver at the 
time when the cardinal system is ‘‘tapped by the hepatic.”’ He 
did not enter into details as to the exact manner in which the tap- 
ping took place, except to remark that ‘‘the right subeardinal and 
hepatic sinusoids approach one another and unite, thus forming a _ 
new access to the heart.” 
Dating from Thoma’s paper upon the vascular area of the chick, 
a new idea of the development of vessels has arisen—namely, that 
they develop from pre-existing capillaries or capillary plexuses. 
Thus every advance of the vascular system is preceded by a skir- 
mish line of growing capillary buds. The work of Aeby and of 
