Fig. 5. Drawing of an embryo with prominent mesencephalic cranial flexure but before formation of the pontine flexure. The optic vesicles have formed eyecups, and the lens is present. The stippled area indicates neural crest. Dotted lines drawn from the neural folds show regions either previously traversed or currently occupied by crest cells that originated from the prosencephalic, mesencephalic, metencephalic, and myelencephalic regions of the neural tube, respectively. Neural crest vacates the dorsal mesenchymal regions around the neural tube and extensively populates the periocular region, branchial arches, and outflow tract regions of the heart.