464 David M. Davis. 
Baader, as early as 1866, had shown the earliest form of this idea. 
Although they stated their belief that vessels arose from capil- 
lary nets, adverse criticism prevented the adoption of this view 
for many years. It was advanced by Mall in 1898 and again in 
1905, in his work upon the liver. Miller and Rabl have also 
supported this view, and lately the work of Evans upon this 
subject has been very convincing. His résumé will give addi- 
tional information on the subject. (Anat. Record, 1908, p. 411). 
PRESENT INVESTIGATION 
When the time is ripe for the formation of the vena cava, the 
situation is such that, for its establishment, it is only necessary for 
a channel to penetrate a very narrow bridge of tissue between two 
already functioning venous trunks. These two trunks are, first, 
a branch of the hepatic vein, and second, the right subcardinal 
vein. To show that this penetration takes place through the 
medium of capillary outgrowths, is a purpose of this study. 
The material used consisted of pig embryos. The following 
table gives data concerning the specimens reconstructed, and the 
numbers by which reference is made to them. 
Table of embryos used in this work 
THICKNESS OF 
SECTIONS IN 
MICROMILLIMETERS 
NO. OF | LENGTH OF 
EMBRYO EMBRYO IN INJECTED BY | INJECTION MASS STAIN 
(MILLIMETERS) 
i | . . 
73) 0) as eee 7.5 Dr. Evans. | Indiaink ~—-50 Haematoxylin 
2302 ee sae 8. Dr. Evans. | India ink 100 None 
23090, Seas 9.5 Dr. Evans. India ink 30 Alum Cochineal 
5} Vere amet 5 illo, 74 writer | India ink 100 None 
The reconstructions were made by the profile method, in which 
tracings upon transparent paper are superposed. ‘This gives a 
flat reconstruction, from which the drawing is worked up. 
A number of other specimens, either in the collection of the 
Anatomical Laboratory of the Johns Hopkins University, or 
injected for the purpose, were examined in less detail. 
