Fig. 9. Cranial neural crest cell migration in the lamprey. Orange arrows indicate migration from the midbrain region; blue arrows indicate migration from the rostral hindbrain (anterior to the otic vesicle) or middle hindbrain region; pink arrows indicate migration of cells from the caudalmost region of the hindbrain or the rostral neural tube. Neural crest cell migration from the midbrain and rostral hindbrain appear similar to other vertebrates. In the mid and caudal regions of the hindbrain and the rostral neural tube, migration appears to involve greater rostral to caudal movement of cells than has been described in other vertebrates. Rostral migration of neural crest is also seen in cells emigrating from the caudal hindbrain region. Although morphological markers and expression of a mid-hindbrain marker (Pax2) have allowed us to determine regions within the hindbrain, we are presently unable to determine the posterior limit of the hindbrain (indicated by?), and the boundary between the hindbrain and the neural tube, because of the lack of sufficient markers for this region and the transient nature of rhombomeric constrictions.