DEVELOPMENT OF LOBULE OF PIG’S LIVER a7, 
Thus far I have shown that the terminal hepatic veins always 
keep within the lobules; that each of its new branches is indicative 
of the formation of a new lobule. The portal veins in growing 
spread between the lobules, tending always to keep within a 
certain distance of the central veins. It should not be inferred, 
however, that the growth of the portal veins follows in point 
of time that of the hepatic veins. Both undoubtably grow hand 
in hand, increasing in length and diameter, and branching as 
the increasing parenchyma demands. With the increase in 
the size of lobules, there is ever the tendency to spread the two 
sets of veins further apart and this tendency is at all times being 
counteracted by the formation of new veins. 
The manner in which the new veins develop, that is by a 
widening out of certain sinusoids, has already been described. 
These new veins, according to Mall, grow into those regions 
on the surface of the lobules which are most distally situated 
from the branches of the portal veins, areas which Mall has 
termed ‘nodal points.’ The whole matter of nodal points can 
only be clearly understood from a study of the lobule in its three 
dimensions; they are uncircumscribed areas on the surfaces of 
the lobules which lie between the terminal branches of the por- 
tal veins and between the central vein of one lobule and that of 
an adjacent lobule. In the dividing lobule shown in figure 26 
as many as ten nodal points may be counted, one of which is 
just forming coincidentally with the formation of the new divid- 
ing septum. The statement of Mall’s (06) that the portal and 
hepatic veins alternately grow toward the nodal points and 
break them into fragments to form new nodal points holds good, 
according to my observations on the pig’s liver, for only the por- 
tal veins. In figure 26 the whole upper surface of the lobule 
was originally represented by a single nodal point; the new 
branch of the portal vein has broken it up into two new ones. 
But the terminal hepatic veins always lie within the lobules, they 
grow toward the nodal points only as the parechyma of the 
lobule increases, but they never reach them. In the lobule 
represented in figure 26 the single central vein H was originally 
directed toward the single nodal point of the top surface, but 
THE AMERICAN JOURNAL OF ANATOMY, VOL. 25, NO. 3 
