THE STRUCTURE OF THE LIVER OF VERTEBRATES

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Abstract
This analytical study, together with observations based on a consideration of the three-dimensional character of tissues led to the conclusion that the livers of vertebrates (except for older Ammocoetes larvae) are not tubular glands, but are solid masses of hepatic cells, perforated by more or less cylindrical lacunae which contain the sinusoids. The walls separating neighboring sinusoids (hepatic plates = laminae hepatis) are predominantly 2 cells thick. In the domestic fowl all hepatic plates are two cells thick; in the meadow-lark they are all one cell thick. In the mammals from Monotremata through Marsupialia to Placentalia they are all one cell thick. Reduction of plate thickness from 2 cells to one is an essential advance from a mechanical and physiol. viewpoint. It can, perhaps, be assumed that reduction in thickness of the liver plates together with development of a cytozonal biliary network has been an important contribution to the evolution of mammals.