English: The head-region of an Amphibian A, and an Amniote (mammal) B, showing segmentation. The broken line o-o indicates the hind limit of the occipital region. 1-7 myotomes. a. Auditory capsule, br.s. Bronchial slit. f. Facial nerve. gl. Glosso-pharyngeal. h. Hypoglossal. h.m. Hypoglossal musculature, n.a. Neural arch. n.c. Nasal capsule, o.p. Optic capsule, s. Tympanum, s.g. Vestigial spinal ganglion, s. o. First metaotic somite, sp. Spinal nerve. tr1. Profundus, tr2 Trigeminal. v. vagus nerve. Diagram 6 of Plate 15 from Metameric Segmentation and Homology