[Distribution of myelinated fibers in the outer plexiform layer of the optic tectum in the frog, Rana temporaria].

Distribution of myelinated nervous fibers in the layer 9 of the optic tectum of the frog Rana temporaria has been investigated in normal animals as well as 6--9, 60 and 134 days after contralateral enucleation. Counts were made on long and oriented sections at the screen of electron microscope. Fields of myelinated fibers in the layer 9, visible under light microscopic, are not distinguished by higher density of these fibers and differ from the other parts of sections probably due to some qualitative differences, especially because of parallel orientation of these fibers within a field. In rostral part of the tectum, myelinated fiber density in the most superficial zone of the layer 9 (0--50 millimicrons from the outer surface) is higher as compared with central and caudal parts. After degeneration of myelinated optic fibers, there are many unchanged fibers of this type in the layer 9.