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86 A Study of the Structural Unit of the Liver 
the imagination of the investigator can patch them together, correctly 
or not as the case may be. But the final evidence is obtained by studying 
serial sections of early livers, where the same vessel can be followed from 
stage to stage. 
The very first vessels that grow into the nodal points in the human em- 
bryo are shown in Fig. 25 from a specimen of the end of the fifth week. 
The vena cava and the vena hepatic media on the hepatic side and the 
ramus arcuatus, the ramus descendens and the ramus angularis from the 
portal side are new vessels. All of the branches of the main trunks with 
the branches of the second order are shown in the reconstruction, 
Fig. 28, and in the section, Fig. 27. Here the new branches of the 
hepatic alternate with those of the portal, each newly-formed field, as it 
is formed, receiving its proper branch in the next stage. The best ex- 
ample is the vena hepatica media in an early stage and the rest of the 
main trunks and their branches as they arise in order. 
There are as many nodal points as there are portal units, and more 
than there are lobules, unless the complex lobule is cut into blocks. The 
arrangement is shown in Fig. 38, which shows one lobule with six ter- 
minal portal veins encircling it. If it is considered that these veins are 
related to adjoining lobules, an estimation of two terminal portal veins 
to one hepatic, as I have it in my table, is not far from being the correct 
number. The reconstruction shows that terminal portal twigs run paral- 
lel, recur again, and run at right angles with the intralobular vein. If 
the portal units are imagined around the interlobular veins of Fig. 38, 
it is seen that both apex and base of the same lobule may represent the 
distal ends of different units. Adjacent intralobular veins and nodal 
points mark the outline of the portal units. 
RELATION OF THE HEPATIC ARTERY TO THE PorRTAL UNITS. 
There always has been and still is much confusion regarding the dis- 
tribution of the hepatic artery and the reason for this is very evident 
when it is considered that it communicates at its end directly, and pos- 
sibly indirectly also, with the capillaries of the lobule. To test this ques- 
tion thoroughly, I have made numerous single, double and triple injec- 
tions with granular and fluid substances in order to determine the courses 
the arterial blood may take during life. 
Long ago Ferrein stated that there were two kinds of branches of the 
portal vein within the liver, one which conveyed blood to the lobule and 
