[Experimental anatomic study of the topography of the retinofugal projections in Discoglossus pictus (Amphibia, Anura). II. The tectum: existence of a double-system of primary optic projections].

The possibility of retinotopic organization of bilateral retinotectal projection was studied by fotal retinal lesions followed by the Fink-Heimer technique. This work in Discoglossus pictus (Amphibia, Anura) shows two types of direct visual projections: a contralateral projection within the tectal layer 9 and a bilateral projection on tectal layer F of Potter (1969). The ipsilateral projection within tectal layer 9, earlier described after enucleation (Picouet et Clairambault, 1977), is not observed here. We discuss about reasons we failed to reveal it. Although appearing to be grossly in accord with data of literature, the retinotopic pattern of "classical" retinotectal projection (on layer 9) of Discoglossus presents some differences as the overlap of quadratic retinal projections. The anatomical tectal retinotopy appears less precise that physiologic retinotopy. The bilateral projections on layer F are characterised by medial (and specially medioposterior) location and the complete absence of retinotopy. All lesions in different parts of retina lead degeneration which take place in a series of distinct loci in the dorsal layer F. We discuss about a possible participation of axial optic tract to this projection.