Structural organization of the optic tectum of Barbus meridionalis Risso. II. Outer strata (SFGS, SO and SM)

The present work deals with the histological organization of the three outer strata of the optic tectum of Barbus meridionalis. As far as general features are concerned, of noteworthy interest are the absence of myelin in the SM and the ordered pattern of myelinic distribution of the SO. The SFGS shows a more irregular appearance than the SM and SO. It was only possible to observe with clarity several neuronal types in the SO and SFGS, whereas in the SM no clear neuronal types could be seen. The SFGS was seen to contain pyramidal neurons with spiny dendrites in the SM, together with fusiform, multipolar and horizontal neurons. In this latter type we have described neurons with ascending axons emerging from the soma or from the base of a principal dendrite. The SO contains neurons whose dendrites are distributed mainly on the horizontal plane, in each case showing certain particular features.