Distribution of types of neurons in the optic tectum of the small-spotted dogfish, Scyliorhinus canicula L. A Golgi study.

The distribution of neuronal types in the six layers of the optic tectum of the small-spotted dogfish, Scyliorhinus canicula, was studied using Golgi methods. The eight types of neurons have a variable distribution, some of them represented in all six tectal layers. Most neurons of the optic tectum have a radial orientation, and a small portion are disposed horizontally. The relative ratios of the different neuronal types in the six layers indicate that about 80% of the tectal neurons are intermingled with the optic nerve axon terminals in the superficial layers of the tectum. These results corroborate previous reports that the tectum of this selachian species is more specialized than formerly supposed, in spite of the differences in degree of neuropil lamination with other non-mammalian vertebrates.