STUDIES ON THE CHIEF VEINS IN EARLY PIG 
EMBRYOS, AND THE ORIGIN OF THE VENA 
CAVA INFERIOR 
DAVID M. DAVIS 
From the Anatomical Laboratory, Johns Hopkins University 
WITH THREE TEXT FIGURES AND SIX PLATES 
INTRODUCTION 
The vena cava inferior has always excited a good deal of interest, 
on account of its unusual history and great importance. When 
its channel first becomes patent, a great change takes place in the 
circulatory system of the embryo, and in a very short time—a few 
hours, in fact—the new vein is carrying practically all the blood 
from the posterior part of the body. Owing to this circumstance, 
the vein, by the time the older investigators observed it in stained 
sections, had already attained considerable size. It was thought, 
therefore, that an attempt to correlate its earliest origin with the 
new theory of capillary or capillary plexus anlagen for the vessels, 
as recently presented by Dr. Evans, would be of interest. The 
notions formerly held will be understood from the following short 
historical sketch. 
HISTORICAL 
In 1888 the result of the work that had been done upon the 
development of the cava to that time, was summed up by Lock- 
wood and Humphry in these words—‘‘It (the vena cava inf.) 
commences a little in front of these organs (kidneys) by two blind 
symmetrical rootlets (the ‘‘renal’’ veins) situated at the base of 
the mesentery and in front of the aorta. After communicating 
with both posterior cardinal veins, especially with the right, it 
runs forward by the side of the aorta, and enters the liver and runs 
through the substance of that organ to empty into the r. vitelline 
vein in front of the junction with theductusvenosus arantii. The 
THE AMERICAN JOURNAL OF ANATOMY, VOL. 10. No. 4. 
