Fig. 6.

Changes in the morphology of the embryo in the embryonic period. The formation of the neural tube occurs between E19 and E29. a. The emergence of the neural ridges is observed on E19. b. The ridges fold over to begin the process of neural tube formation. c. Closure of the neural tube begins on E22 in central regions of the newly forming neural tube. d. Closure continues in rostral and caudal direction. The anterior neuropore closes on E25, and the posterior on E27. e. Following the closure of the neural tube, the embryo begins to expand particularly in anterior regions. The primary vesicles are evident by E28. These include the Prosencephalon, Mesencephalon, and Rhombencephalon. f. By E49 the secondary vesicles emerge. The Prosencephalon differentiates into the Telencephalon and Diencephalon, and the Rhombencephalon into the Metencephalon and Myelencephalon. Illustrations by Matthew Stiles Davis reprinted by permission of the publisher from THE FUNDAMENTALS OF BRAIN DEVELOPMENT: INTEGRATING NATURE AND NURTURE by Joan Stiles, Cambridge, Mass.: Harvard University Press, Copyright © 2008 by the President and Fellows of Harvard College