The abducens nucleus in the carpet shark Cephaloscyllium isabella

This study utilizes retrograde axonal transport of cobaltous-lysine, and conventional silver and Golgi staining techniques to study the abducens motor nucleus innervating the external rectus muscle of the carpet shark. The nucleus consists of 300-400 motoneurons located immediately ventrolateral to the medial longitudinal fasciculus (MLF), distributed over about 1.25 mm in a rostrocaudal direction at the level of exit of the VI nerve. The axons of the motoneurons form seven or eight discrete ventrally directed fascicles which, having exited from the brainstem, group together to form the abducens (VI) nerve. The motoneurons are on average about 16 micron in diameter, are bipolar, and their dendrites have a transverse orientation. Typically one set of dendrites penetrates the MLF and the other set extends ventrally into the reticular formation.