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Abstract:
The projections of long visual fibres (R7+R8) from the retina to the medulla and their levels of termination in the second synaptic region have been studied with the aid of light and electron microscopy. Normal and degenerated material has revealed the fine structural characteristics of the long visual fibres as well as their orientations relative to those of a pair of first order interneuron terminals (monopolar cells). R7 and R8 project as pairs across the first optic chiasma. Their position equatorial to monopolar cells in the lamina is shifted to a polar position in the medulla via the chiasma. Their endings are situated at two levels: namely, R7 is deeper than R8. Like the short visual fibre endings in the lamina (R1–R6) the terminals of R7 and R8 in the medulla have synaptic specialisations throughout their length. The long visual fibres provide a point for point projection from the retina to the medulla and with monopolar cell terminals are arranged coincident with the three axes of the visual neuropil.
