Fig. 1

Anatomy of EOMs and distributions of head cavities in the shark embryo. a Left lateral view of an adult shark (S. torazame; top) and schematic drawing of the left extraocular muscles (bottom). Sets of EOMs innervated by the same cranial motor nerve are shown in the same color: EOMs innervated by the oculomotor nerve in brown, by the trochlear nerve in orange, and by the abducens nerve in green. The blue dotted line indicates the outline of the left eye. b A schematic drawing of the left lateral view of the shark embryo at st. 25 showing the positional relationships of head cavities (HCs) to the pharyngeal and cardiac mesoderm (dark gray) and somites (light pink). Each HC is marked in the same color as sets of EOMs in (a), which are predicted to be derived from a single HC. c, d H&E sections in the transverse section (c) and the sagittal section reconstructed from serial transverse sections (d), showing the anatomical position of HCs, which are arranged in series dorsoventrally (c) and anteroposteriorly (d). The scheme in (a) is modified from ref. [1]. II, optic nerve; III, oculomotor nerve; IV, trochlear nerve; VI, abducens nerve; gV, trigeminal ganglion; ham, hyoid arch mesoderm; IO, inferior oblique muscle; IR, inferior rectus muscle; LR, lateral rectus muscle; mam, mandibular arch mesoderm; mnc, mandibular head cavity; MR, medial rectus muscle; op, optic cup; ot, otic vesicle; pcm, pericardial mesoderm; prmc, premandibular head cavity; SO, superior oblique muscle; som, somite; SR, superior rectus muscle