[Experimental anatomic study of the topography of the retinofugal projections in Discoglossus pictus (Amphibia, Anura). I. The thalamus: re-examination of the contralateral retinotopy and the origin of the uncrossed optic fibers].

The topography of retinofugal projections on the thalamus of an Anuran Amphibia was studied by Fink-Heimer technique. After small lesions in retina, degeneration was found in all contralateral neuropils and in one or several ipsilateral neuropils according to retinal location: A lesion in temporal retina is followed by large axonal degeneration in neuropil of Bellonci; a dorsal lesion invaded whole geniculate neuropil while within it, contralateral ventral and nasal projections are scarce. Ipsilaterally, excepted for the nasal retina, all territories project to anterior neuropils; but, only temporal fibres ended in ipsilateral pretectal neuropil. The incinate neuropil receives bilateral projections from the whole retina. This study shows that, rather than a strict segregation, an overlap of quadratic projections into the same neuropil and a divisional repartition of these projections between the two anterior neuropils seem to be the rule.