Original study and a review of the pertinent literature are presented in this monograph on the early development of the neopallial wall and the choroidal area in vertebrates before the appearance of nerve cells. In the pre-neural period the telencephalic wall is a cohesive, non-stratified epithelial sheet of elongated, radially oriented, polarized cells. Although these cells, including the radial glial cells, differ from each other in various regions and change in shape, internal structure and phenotypic expression during development, they have a basic unity. The book draws attention to this unity and discusses the cells' morphogenesis and functions, and the mechanisms which help to shape the early cerebral hemispheres. The pre-neural period is of fundamental importance for the development of the cerebrum. The knowledge presented here of how cells differentiate during the early stages will help neuroscientists by providing a basis for comparisons with cultured cells and explants, and with cells seen in lineage studies and with microscopic observations of living animals in which dynamic events in the CNS can be seen directly. This work will improve our understanding of many developmental abnormalities of the nervous system.