The Spinal Nerves of the Dogfish (Scyliorhinus)

Abstract

The locomotory musculature of dogfish is innervated by the segmental spinal nerves. The sensory and motor innervation of the abdominal musculature was studied in a preparation consisting of a strip of the abdominal body wall innervated by the ventral rami of the spinal nerves.Each ventral ramus consists of two separate nerve bundles which were found to be peripheral extensions of the dorsal and ventral spinal roots. Recordings from the sensory bundles showed that there are few sensory endings in the musculature and body wall of the dogfish. It was possible to differentiate between ephemeral responses produced by cutaneous free-nerve endings and prolonged discharges which were generated by more specialized sensory endings. In some details these endings were found to be unlike either muscle spindles or tendon organs. Further, skinning experiments suggested that these mechanoreceptors lay in the skin or the very outer layers of the myotome.Histological searching, together with physiological isolation of units, suggested that these receptors were the corpuscular endings distributed sparsely amongst subcutaneous tissue. These endings are apparently the same as those described by Wunderer (1908) in the fins of elasmobranchs.