Rendering of the embryologic development of the fourth ventricle Rendering of the embryologic development of the fourth ventricle.Axial section of a 27-mm human embryo (approximately day 56 and Carnegie stage 22) shows ventral fourth ventricular furrow (arrow) deeply indenting the posterior aspect of the developing meten... Rendering of the embryologic development of the fourth ventricle.Axial section of a 27-mm human embryo (approximately day 56 and Carnegie stage 22) shows ventral fourth ventricular furrow (arrow) deeply indenting the posterior aspect of the developing metencephalon.Modified from M. Hill, UNSW Embryology, version 3.0 (8), with permission. Andrea Rossi et al. AJNR Am J Neuroradiol 2004;25:1046-1048 ©2004 by American Society of Neuroradiology