On the occurrence of an intracranial ganglion upon the oculo-motor nerve in scyllium canicula , with a suggestion as to its bearing upon the question of the segmental value of certain of the cranial nerves

Abstract

During the study of a number of elasmobranch brains made in connection with my work on Reissner’s fibre, I noticed, in a specimen of Scyllium canicula , a collection of ganglion cells upon a length of nerve lying freely beneath the mid-brain. This particular brain had been sectioned in the longitudinal vertical plane and the ganglionic mass occurred at a place which corresponded with the level of the third cranial nerve. Further examination showed that these cells were undoubtedly related to the oculomotor nerve. They are situated upon it in a scattered group which, beginning at a point about 1·4 mm. from the superficial origin of the nerve, stretches to its severed end (roughly 1·6 mm. from its origin). The cells, though only about 15 in number, are moderately large (averaging 20 μ × 18 μ ) and are apparently unipolar or bipolar. Their distribution suggested that other cells of the group must have existed distally to the point of severance of the nerve. Upon the opposite side of the brain the corresponding nerve had been cut away quite close to its superficial origin, when the brain was removed from the cranium.