It is well to begin the study of the peritoneal connections of the liver with the consideration of the embryonic stage shown in [Fig. 273] schematically.

Fig. 276.—Schematic view of embryonic liver detached from its connections, seen from behind, with lines of peritoneal reflection.

If we imagine this embryonic liver detached from its connections in such a manner as to leave the divided peritoneal layers of the ventral mesogastrium as long as possible, and if we regard the preparation from behind, the appearance of the parts could be represented in Fig. 276.[6]

It will of course be seen that the area of direct adhesion to the diaphragm, extending transversely, would separate the lesser omentum from the suspensory ligament.

As is seen in the transection ([Fig. 274]), the right and left layers of the suspensory ligament, at its attachment to the liver, turn into the visceral peritoneum investing the organ on its ventral and cephalic surfaces. Continuing around the borders of the liver this visceral peritoneum then invests in like manner the dorsal or caudal surface directed toward the stomach, until, at the region of the future portal or transverse fissure, this visceral peritoneum becomes in turn continuous with the two layers of the lesser or gastro-hepatic omentum. Consequently in the embryonic detached liver the lines of peritoneal reflection would be nearly cruciform, the vertical limb of the cross being formed on the cephalic surface by the two layers of the suspensory ligament, while on the caudal surface it is formed by the layers of the lesser omentum. The horizontal arm of the cross is formed by the upper and lower limits of the area of diaphragmatic attachment, along which the parietal diaphragmatic peritoneum turns into the visceral hepatic investment (forming the two layers of the primitive coronary ligament). In the liver shown thus schematically from behind we would overlook the dorsal and adjoining portions of the cephalic and caudal surfaces of the adult human liver.

The primitive biliary duct, portal vein and hepatic artery reach the liver between the layers of the lesser omentum. The venæ revehentes (hepatic veins) reach the sinus venosus at the attachment of the liver to the septum transversum (primitive diaphragm).

The first important change, resulting in a rearrangement of these peritoneal layers, is produced by the connection of the umbilical with the rudimentary portal vein.

Fig. 277.—Schematic view of embryonic liver, showing influence of vascular connections on the arrangement of the lines of peritoneal reflection.
Fig. 278.—Later stages, showing development of transverse fissure, Spigelian and caudate lobes.

This junction occupies a relatively wide area on the caudal surface of the liver, and the layers of the lesser omentum are separated somewhat at this point to accommodate the enlarging vascular structures between them. More especially is this the case with the right leaf of the primitive gastro-hepatic omentum. A species of lateral diverticulum is formed by this leaf so as to include the umbilical vein at its junction with the portal. The membrane in the region of this diverticulum turns its surfaces dorsad and ventrad, and its free edge toward the right (Fig. 277). With the gradual increase in the size of the vessels, and with the transverse position which the rotation of the stomach imparts to the opposite border of the lesser omentum attached to the lesser curvature, this transversely disposed portion gradually exceeds in length and size the part of the original omentum enclosing the umbilical vein. This vessel and the investing peritoneum become lodged in a sagittal depression on the caudal surface of the liver (rudimentary umbilical fissure), while the transverse portion, developed as indicated, surrounds the structures connected with the liver at the future transverse or portal fissure.