The development of hippocampal and dorsolateral pallial regions of the cerebral hemisphere in fetal rabbits. III. Twenty‐nine millimeter stage, marginal lamina

The structure of the cerebral hemisphere of 29 mm rabbit embryos was stuided with aniline and Golgi stains. Particular attention was devoted to the structure of the marginal lamina. In aniline stained sections it is a light, relatively acellular layer at the surface of the embryonic cerebral hemisphere and corresponds to layer I, the molecular layer, of the adult cerebral cortex. Even in early embryonic stages the marginal lamina consists mainly of terminal remifications of pyramidal cell apical dendrites and ascending axons. This layer of neuropile is of particular interest since it greatly precedes the development of other cortical zones rich in axons and dendrites. The reasons for the precocious development of dendritic branches at this level are unknown but may be related to the presence of ascending axons of nerve cells in the cortical plate or to horizontal cells. Large and small horizontal neurons are the only intrinsic cells at this level. Axons are present on the small elements, but were seen only infrequently on large cells. Some of the latter are similar to Cajal‐Retzius cells of perinatal stages, but have relatively few ascending branches.