Franklin P. Mall - 261 
The right omphalo-mesenteric vein is still present and the ductus venous 
is well marked. In this case the liver is formed of four main lobules, 
and with the subdivision of the middle and left hepatic veins into two 
branches each, six primary lobules are seen to correspond with the six 
primary lobes of the mammalian liver. In this case the vena hepatica 
dextra superior et inferior is represented by the open omphalo-mesenteric 
vein and the anlage of the vena cava inferior. In the next stage, Figs. 
26 and 28, the normal arrangement of these veins is found for the vena 
cava inferior really belongs to the middle lobe. 
Fig. 20. 
Fig. 19. Section through the embryo 9 mm. long (No. 163). x 12%. 
C,, eighth cervical myotome; pp, pleuro-peritoneal membrane. 
Fic. 20. Ventral view of the veins of the liver of the embryo 9 mm. long 
(No. 163). JL, liver; i, intestine; wv, umbilical vein; vp, vena portae; g, gas- 
tric vein; m, mesenteric vein; ra, ramus angularis; ra,, ramus arcuatus; rs, 
ramus sinistra; rd, ramus dextra; dv, ductus venosus. 
With the completion of six lobules we recognize fully the adult form of 
the liver. Each lobule now represents one of the six lobes of the mam- 
malian liver; each of the primary lobules is to expand into a whole lobe. 
The primary lobules radiate from a center and have between them the 
