Figure 1. Occipital region in actinopterygian fish.

(a) Cranio–vertebral junction (asterisk) in a juvenile midshipman stained with alcian blue and alizarin red. (b) Hindbrain–spinal cord boundary (yellow hatching) demarcated in the zebrafish hoxb4a enhancer trap line. (c) Pectoral fin innervation in juvenile midshipman. (d) Schematic drawing of c showing occipital nerves (Oc, red, orange and brown in d) exiting through occipital foramen (OcF) located anterior to the cranio–vertebral junction, and spinal nerves (Sp, black in d) exiting through vertebrae (V). (e) Embryonic alignment of caudal hindbrain, fourth ventricle, otic vesicle (OV) and myotomes (M) (includes blue lipophilic dye injection in fin buds; midshipman fish). The location of pectoral motoneurons is also indicated. NE, neuroepithelium. Images are dorsal (a, b, e) and ventral (c, d) views with anterior to the left. Scale bars are 1 cm (a), 200 μm (b), 500 μm (c, d) and 100 μm (e).