314 FRANKLIN PARADISE JOHNSON 
lobule into two new ones, one of which is supplied by the old 
central vein, the other by the new one. That new branches 
of both the hepatic and portal veins arise as outgrowths from 
the main trunks is stated by Mall. 
Surface lobules often divide by the combination of the two 
processes just described. The long axes of such lobules are 
placed at right angles to the surface of the liver. When a sur- 
face lobule divides its central vein bifurcates, the new branches 
spread apart and then bend to become perpendicular to the 
surface (fig. 23). A septum then starts from the surface, mid- 
way between the two new branches, and grows down to the 
fork of the central vein. Thus two elongated lobules are marked 
off. These then become cut up transversely, new branches 
from either the new or old central veins extending in to the 
lower ends of the lobules. In some instances, however, the 
new hepatic veins which supply the lower ends of the lobules 
are formed earlier by a bifurcation of the new central vein. 
Slight variations in development are often met with in cer- 
tain groups of new lobules. Figure 24 is from a wax recon- 
struction of three almost completely formed lobules which have 
developed from a single one. The original central vein H has 
bifureated into the two branches h and h. The original septum 
is shown between A and H; it is almost complete. A new cleav- 
age, B, however, has grown in from the side and has joined the 
original septum, thus completely cutting off the lobule VN. A 
new vein, h’, has grown out from the original central vein into 
the new lobule O, which is not yet entirely separated from the 
lobule M. In the process of splitting, the original central vein 
H has become interlobular in position. 
Very seldom in the pig’s liver is found a lobule through which 
the central vein extends to become the central vein of another 
lobule. One of the few which I have found in looking over 
a large number of lobules is shown in figure 25. Judging by 
the stage of development of its connective tissue septa, I have 
explained its existence in the following manner: The three 
lobules, A, B, and C, were originally one: its central vein H 
bifureated into h and h, and the longitudinal septum grew 
