The neural organization of the first optic ganglion of the principal eyes of jumping spiders (Salticidae)

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Abstract
The first optic ganglion (FOG) of the principal eyes of jumping spider has been studied by both light and electron microscopy. Each FOG receives projections from the ipsilateral principal eye in a compact optic nerve. Some of the retinal axons, as they pass to the ganglion, cross in a chiasm within the optic nerve. The FOG is composed of a rind of nerve cell bodies which are unipolar cells giving rise anteriorly to second order nerve fibers in the central neuropile of the ganglion and posteriorly to processes which pass into the second optic ganglion. The neuropil is composed of neural and glial processes and of scattered glial cell bodies and it can be divided into a terminal zone and a fibrous zone. The terminal zone is the site of termination for all of the retinal axons. A unique feature of the retinal axon terminals is the presence of numerous fine post‐terminal processes extending away from the main portion of the retinal terminal. The fibrous zone is composed of second order nerve fibers with terminals in the terminal zone and it is continuous with a connective between the FOG and the second optic ganglion called the chiasm where the majority of the second order fibers cross.All of the synapses in the FOG are modified ribbon synapses and occur in the terminal zone within ensheathed synaptic glomeruli as dyads or triads. Large retinal terminals containing pleomorphic vesicles are presynaptic to smaller second order terminals containing spherical vesicles. Second order terminals are also presynaptic to retinal terminals in addition to forming serial‐like synapses with each other.