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Liver development in the rat during the embryonic period (Carnegie stages 15-23).

Hepatic and biliary structures appearing during embryonic Carnegie stages 15-23 were analyzed in OFA rat embryos. The group of rats with crown rump length 7.5-16 mm and 12.8-16 days after coitus yielded 55 specimens (23 of stages 15-16, 20 of stages 17-18, 9 of stages 19-22 and 3 of stage 23). The embryos were submitted to serial histological sections with graphic reconstructions. From stage 15 to the end of the embryonic period, the hepatic gland and its vascular channels (transverse portal sinus and hepatocardiac veins) presented considerable enlargement while hematopoietic function appeared. At stage 17, occlusion due to epithelial proliferation was evident in the hepatic duct. At stage 18, the duct became recanalized and assured the continuity between liver cells and gut. From stage 18 to 23, biliary ductules developed in periportal connective tissue forming ductal plates which received biliary caniculi. Except for the gall-bladder which is never present in the rat, similarity and presence of the same hepatic structures in man and in the rat during the embryonic period stages 15-23 suggest that the rat is a good experimental model for liver development and will be useful in the understanding of congenital anomalies.