Besides the main leg-nerve there is, in spiders, a ‘small leg-nerve’ which is mainly sensory. About 8 of the fibres arise from neurones which form a ganglion at the femurpatella joint and appear anatomically to be joint mechanoreceptors, but if so must supplement the lyriform organs. Cutting the small leg-nerve has no effect on the walking pattern nor on the detection of prey, which almost certainly depends on mechanoreception. The small leg-nerve contains one motor fibre which innervates the claw elevator. This muscle has a double innervation, a second fibre running in the main leg-nerve. There are interesting parallels between the small leg-nerve in spiders and Limulus.

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