Franklin P. Mall . 259 
proportion. All through the organ the terminal twigs of the distributing 
and of the collecting veins must not be over a millimeter apart, and this 
naturally keeps the units small and determines the ratio between the 
terminal twigs and the capillary bed. 
In the embryo of the end of the fifth week, Fig. 25, the right and left 
portal twigs have begun to divide, and from the recessus umbilicalis a 
Fig. 15. Lateral reconstruction of a human embryo 7 mm. long (No. 2). 
L, liver; ph, phrenic vein; 1, 2, 3, 4, branchial pouches; Roman numerals, 
cranial nerves; Arabic characters, spinal nerves. 
new group of veins have formed and radiate into the middle and left 
lobes of the liver. On the hepatic side the left branch has divided into two 
trunks and two new branches have appeared: the vena cava inferior and 
the vena hepatica media which has its terminal right and left branches. 
20 
