Medullary and cerebellar projections of the statoacoustic nerve of the dogfish,Scyliorhinus canicula

Abstract

The statoacoustic nerve of the dogfish, Scyliorhinus canicula, was transected medial to the ganglion for the purpose of elucidating its central pathways and terminal fields. Following two to six weeks postoperative survival times, transverse, horizontal, and sagittal sections of the brain stem were stained by the Fink‐Heimer silver‐impregnation method to reveal degenerating axons and terminals. Fragmented axons enter the medulla and give rise to medial, descending, and ascending pathway. Fibers of the medial pathway terminate about the soma and lateral dendrites of the large cells that comprise nucleus magnocellularis; descending and ascending flbers terminate on the dendrites of the cells of ventral and superior nuclei respectively. In addition, fibers emanate from fascicles of the descending pathway to form a large field of degenerating axons and terminals within the ventromedial part of the medulla, and a substantial proportion of the fibers of the ascending pathway continues beyond the superior nucleus to terminate among the granule cells of the medial part of the vestibulolateral lobe of the cerebellum. No fragmented axons are traceable to the lateral part (auricles) of the vestibulolateral lobe, cerebellar nucleus or corpus, or those nuclei associated with the lateral‐line lobes. It appears therefore that octavus terminal fields are separate from those of the lateral line at both cerebellar and medullary levels, at least at the level of the first‐order neuron.