Histogenesis

Abstract

The neural plate and early neural tube are formed by a single layer of columnar cells, the neuroepithelium (Fig. 5.1a). As this layer thickens it gradually acquires the configuration of a pseudostratified epithelium; that is to say, its nuclei become arranged in more and more layers, but all elements remain in contact with the external and internal surface (Figs. 5.1b, 5.2, 5.3a). Mitotic figures are found exclusively along the ventricular surface (Fig. 5.1). His (1889) believed that these mitoses belong to cells which form a ventricular layer of germinal cells (Keimzellen), and that the more peripherally located cells represent spongioblasts, primordial glial elements forming a syncytial meshwork (Markgerüst). Neuroblasts produced by the germinal cells were supposed to migrate peripherally in the intercellular spaces of this meshwork.