[Embryonic development of the brain of Scyliorhinus canicula (L.). III. The optical system and adjacent nuclei in the tegmentum mesencephali].

The ontogenesis of the optic system in the brain has been studied with reference to the general biology of the embryo and to the cytoarchitecture of the optic tectum. 1. Sharks vary in terms of retinal structure (Franz 1931). Scyliorhinus shows densely packed and large cellular layers alternating with thin fiber layers. 2. The optic tracts, which are not excessively large, cross in the optic chiasm by approximately 95%. The optic fibers, forming a medial and a lateral tract, enter the tectum in zones 9 and 11. 3. The eye muscle nuclei do not differ from the general vertebrate pattern. The oculomotor nucleus represents the largest portion; the abducens nucleus is small. 4. The nucleus interstitialis of the fasciculus longitudinalis medialis is remarkably developed and consists of large neurons. Together with the interpreduncula nucleus it receives fibers of fasciculus retroflexus.