DEVELOPMENT OF LOBULE OF PIG’S LIVER pied 
hepatic vein, as pointed out by Mall. In their growth they 
bear a certain constant relation to the growing hepatic veins, 
through which relation a constant flow of blood is maintained. 
In figures 8 to 10 are shown hepatic lobules in successive 
stages of development. Figure 8 is a section of a slightly elon- 
gated lobule with a bifurcating vein. Although in all other 
respects this lobule is similar to other single lobules, it can be 
definitely stated, because of the branching of its hepatic vein, 
that it has begun to divide. In figure 9 the new branches of 
the central vein are longer, having kept pace with the length- 
ening lobule. The new veins grow, as described by Mall, by 
the enlargement of certain sinusoids. In addition to the new 
veins is to be seen the beginning of a cleavage of the lobule. 
This is represented by the arrangement of certain hepatic cells 
into parallel rows, between which collagen fibrils later appear. 
It is to be noted that the septum occupies the plane of the orig- 
inal central vein and bisects approximately the angle formed 
by its two new branches. The free edges of the septum lie 
just above the fork of the central vein, which position (fig. 9) 
it maintains for some time. 
That the new central veins lengthen in many instances at 
the expense of the old one, that is, by cleavage of the latter, 
there is little doubt. In those lobules in which the central 
vein is just beginning to bifurcate it is relatively long; in those 
in which the branches are long the old central vein is usually 
shorter. This apparent splitting of the old central vein seems 
to be caused by the growth of the septum into the fork of 
the central vein. In many instances where the cleavage of a 
lobule is nearly complete the old central vein is split down 
almost to the point where it enters the lobule. 
The further separation of the lobule into two new ones takes 
place slowly by the continued growth of the new septum from 
the sides of the lobule toward the old central vein. When the 
septum is complete, the remaining portion of the old central 
vein is found to he between the two new lobules; it may then 
be spoken of as a small sublobular vein. 
