[Embryonal development of the brain of the shark Scyliorhinus canicula (L.). II. The optic tectum and its stratification].

The stratification of the optic tectum of the shark Scyliorhinus canicula is comparable to patterns of other vertebrates. Thus it is possible to homologize part of the cortex layers with those described by P. RAMON (1896) and HUBER & CROSBY (1933b). 1. As for other vertebrates, it makes sense to collect the large number of zones (layers) into three groups: periventricular, central and superficial. 2. Ramon's periventricular zones 1--3 are distinct; fibrous zone 4 and cellular zone 5 are partially mixed. The central zones (6, 7) are mixed. All superficial zones are recognized, with the exception of zone 14, which was not found. 3. The trigeminal mesencephalic nucleus develops in the early embryo.