Fig. 10. Summary indicating the proposed route of migration for the gnrh3 cells of the terminal nerve and the gnrh2 cells of the midbrain. (A) Terminal nerve gnrh3-expressing cells (arrow) arise from cranial neural crest and migrate rostrally dorsal to the eye (D, purple arrow, a) to join the forming olfactory placode (D, red). (B) Midbrain gnrh2 cells (arrows) lying on either side of the midline (arrowhead) also arise from cranial neural crest and migrate posterior to the developing eye (D, purple arrow, b). (C) Hypothalamic GnRH cells (arrows) arise from the anterior pituitary region [D, orange (see Whitlock et al., 2003)]. (D) Lateral view of an embryo showing the migration routes (purple arrows) of cranial neural crest. e, eye.