2. Connection of umbilical vein in liver:
(a) With portal system ([Figs. 258] and 271).
(α) With portal vein.
(β) With portal system of left and quadrate lobes by
branches derived directly from umbilical vein
while situated in the umbilical fissure ([Fig. 258]).
(b) With hepatic veins and postcava by the ductus
venosus ([Figs. 258] and 271).
3. Connection of the postcaval and precaval systems by the azygos veins representing the proximal segments of the embryonic postcardinal veins ([Fig. 272]).
Fig. 272.—Human fœtus at term. Postcava and azygos veins. (Columbia University Museum, No. 1861.)
If possible the dissection of an injected fœtus should be combined with the examination of corrosion preparation of the fœtal circulation and especially of the venous system of the fœtal liver ([Figs. 258] and 271).
3. The remnants of fœtal structures in the adult liver (round ligament and ligament of the ductus venosus) should be compared with the structures from which they are derived in the fœtus at term (umbilical vein and ductus venosus).
II. THE VENTRAL MESOGASTRIUM.
This membrane has been heretofore mentioned on several occasions. It now remains for us to carefully consider its arrangement in detail, both as regards the peritoneal relations of the liver and in reference to its influence on the abdominal space as a whole. We can best accomplish this purpose by considering the membrane in the first place in a purely schematic manner. In contradistinction to the primitive common dorsal mesentery, which extends the entire length of the alimentary tube, the ventral mesentery, or properly the ventral mesogastrium, is confined to the stomach and proximal portion of the duodenum. We can represent the membrane as extending between the ventral abdominal wall and the ventral border (later the lesser curvature) of the stomach and of the hepatic angle of the duodenum. Cephalad it is connected with the embryonic septum transversum (future diaphragm). Caudad its two layers pass into each other in a free concave edge, including between them the umbilical vein (free edge of falciform ligament of adult). Consequently a schematic profile or lateral view of the membrane and its attachments in the earlier stages would appear as represented in [Fig. 273], while the arrangement in transection would be as shown in [Fig. 274]. It will be observed that the separation of the cephalic portion of the abdominal cavity into symmetrical right and left halves, previously indicated in discussing the primitive stomach and the dorsal mesogastrium, is actually completed by the ventral mesogastrium. This complete separation of the lateral halves of the cœlom cavity ceases at the point where the ventral mesogastrium terminates in the free concave edge carrying the umbilical vein. Hence caudad of this falciform edge the two halves of the cavity communicate freely with each other ventrad of the intestine and dorsal mesentery.
