This, which is the most internal of the tunics of the eye, is a sheet of nerve tissues situated between the choroid coat and the vitreous humour, specially organized to receive and transmit impressions of light. Its structure (fig. 245) is very complex, but it consists essentially of an outer layer of rods and cones, followed by several layers of cells and nuclei, with interwoven fibres, which give cohesion and strength to the different layers. The fibres of the optic nerve terminate in the retina, and conduct the impressions made upon the retina through the optic nerve to the brain. The accompanying woodcut will sufficiently demonstrate the structure of the retina as now received by the best observers.