Termination of retinofugal fibers and lamination pattern in the lateral geniculate nucleus of the gibbon

The lateral geniculate nucleus (LGN) of the gibbon (Hylobates sp.) consists of four principal layers, i.e., layers 1 and 2 containing large somata and layers 3 and 4 comprising medium-sized neurons. In addition, there are intercalated layers S, imm and imp, each consisting of small cells. Tracing of retinofugal fibers with the autoradiographic method revealed that the retina projects to the ipsilateral layers 2, 3 and imp and to the contralateral layers 1, 4, S and imm. No 'hidden' layers have been found. This type of lamination pattern sets the LGN of the gibbon apart from that of all Old World monkeys, chimpanzee and man. Retinal projections to other subcortical regions are also described.