formation of a free right edge, with the ventral layer of the same membrane, passing from right to left, the two layers including between them the structures entering and leaving the liver at the transverse fissure (portal vein, hepatic artery, duct). Arriving at the left extremity of the transverse fissure the ventral layer of the transverse segment of the lesser omentum--as we practically trace it in the adult as a free membrane--turns directly into the left leaf of the sagittal segment attached along the fissure for the ductus venosus, and becomes continuous along the dorsal border of the left lobe with the caudal layer of the left coronary ligament. This direct continuity, as just stated, exists practically in the adult. From the development of the membrane, however, it will be seen that the ventral layer of the transverse lesser omentum, at the left extremity of the portal fissure, becomes continuous with the right layer of the primitive mesogastrium enclosing the umbilical vein. After surrounding this vein it is continued into the left leaf of the same membrane, which in turn passes into the left layer of the portion attached along the fissure for the ductus venosus. This original connection can at times be traced very clearly in young specimens (Fig. 279), and occasionally is also still evident in the adult liver. Usually, however, the round ligament of the adult and its investing peritoneum is buried so deeply in the umbilical fissure, or even bridged over in part by liver tissue, that the connection is not evident. The ventral layer of the transverse omentum then appears directly continuous with the left layer of the sagittal omentum attached along the fissure for the ductus venosus. We can sum up the facts just considered as follows: 1. The rotation of the stomach from the sagittal into the transverse position, and the development of the umbilical and portal veins, rearrange the original sagittal plane of the lesser omentum, dividing it into two districts: (_a_) Cephalic portion, remaining in the original sagittal plane, follows the fissure for the ductus venosus. With the incorporation of the Spigelian lobe in the adult dorsal or "posterior" surface of the liver, this segment of the omentum assumes a vertical direction, forming the left boundary of the Spigelian recess, being reflected from the fissure for the ductus venosus to the abdominal portion of the oesophagus and the part of the lesser curvature of stomach adjacent to the cardia.