462 David M. Davis. 
vena cava enters the liver through a junction—the caval junction 
—which that organ previously acquires with the tissues at the 
base of the mesentery.” This is practically the description 
given by Kolliker, and His seems to confine his attention to the 
liver veins, commenting only sparingly upon the vena cava. It 
is noticed that little effort is made to explain the exact means by 
which the changes take place. 
The next important writer on the subject was Hochstetter, 
whose first work appeared in about 1888, and covered a period of 
many years. The technique of the time made certain mistakes 
unavoidable, but his descriptions of the morphological changes 
occurring in the already formed veins can scarcely be surpassed. 
Regarding the origin of the cava, he practically reversed the proc- — 
ess, speaking apparently, of it as ‘growing down”’ from the liver 
into the Wolffian ridge, and there receiving bilateral veins drain- 
ing the kidneys and Wolffian bodies. 
As is well known, the veins of the very young embryo are quite 
symmetrical. There are three systems—the vitelline, the umbil- 
ical, and the cardinal, each consisting of two bilaterally symmet- 
rical veins, the three of either side uniting at the duct of Cuvier to 
form the sinus venosus. For reasons as yet unknown, the stom- 
ach shifts to the left in development and the liver confines itself 
mainly to the right side. The stomach, according to F. T. Lewis, 
presses upon and obliterates the left ala pulmonalis (Ravn) where 
it extends into the future abdominal cavity, while the liver 
approaches the corresponding structure upon the right, and 
appropriates it by sending first capillaries, then hepatic tubules, 
into it. This bridge between liver and mesenchyme was called by 
Hochstetter the Hohlvengekrése, and may be designated as 
‘“‘caval mesentery’’ (Lewis). See fig. 2. Hochstetter’s view was 
that the cava grew down through this caval mesentery, and gave 
rise to three branches—more properly roots. One ofthese extended 
caudally upon the right Wolffian body, the other two caudally and 
cranially, respectively, upon the left Wolffian body. These two 
roots upon the left united into a common stalk before crossing, 
ventral to the aorta, to join their fellow of the right. (These veins 
were called the vv. revehentes posterior by Hochstetter, and are 
