DEVELOPMENT OF LOBULE OF PIG’S LIVER o25 
is everywhere growing at an equal rate. While this assumption 
is probably true for groups of lobules taken collectively, it is not 
always true within individual lobules. I have shown above that 
when a lobule grows, it may increase more in one diameter than 
in another. It is probable that this type of unequal growth 
gives rise to local pressures here and there and that these in turn 
determine to a certain degree the shapes of the lobules. 
CONCLUSIONS 
1. The first evidence of connective tissue septa found was in 
an embryo of 254 mm. in length. The growth of the septa is 
gradual and they are not fully formed until about two months 
after birth. Their origin is first indicated by the arrangement 
of the border cells of the lobules in parallel layers. The con- 
nective tissue of the portal canals sends sprouts into the reticulum 
between the layers of border cells. These sprouts, coming from 
opposite directions, meet in the region of the nodal points thus 
completing the septa.- Additional septa are formed with the de- 
velopment of new lobules. Their paths are similarly marked out 
by the parallel arrangement of border cells. The collagen fibrils 
of these septa sprout out from the connective tissue about the 
portal veins and from that of those septa already present. 
2. The collagen fibrils of the capsula fibrosa (Glissoni) appear 
first in the region of the porta hepatis and spread over the sur- 
face of the liver. They completely cover the liver in a pig of 111 
mm. ‘The capsule remains as an extremely thin and delicate 
layer until birth, after which time it gradually thickens. 
3. The formation of new lobules may be described as a neces- 
sary readjustment on the part of the parenchyma to circulatory 
difficulties. It is accomplished by a binary fission of lobules al- 
ready present, the cleavages taking place only in lobules which 
have developed two central veins. The new central veins may 
arise, 1) by a bifurcation of the tip of a growing central vein, or 2) 
by a sprout from the side of an existing vein. The plane of cleav- 
age bisects the angle formed by two new veins. The cleavage is 
evidenced by the arrangement of the hepatic cells into parallel 
