Nervus terminalis in dogfish (Squalus acanthias, Elasmobranchii) carries tonic efferent impulses.

Recordings from the intact nervus terminalis with a hook electrode or from a stump of the divided nerve with a suction electrode show a tonic, irregular discharge of broad, low frequency spikes in ca. 4-6 units. These nerve impulses are efferent from the brain. The mean frequency of discharge is not influenced by various chemical, thermal, tactile, acoustic, photic, vibratory and electric field stimuli but is decreased by certain forms of mechanical stimuli, presumably acting on the lateral line organs of the lateral aspect of the head. We have not succeeded in recording from afferents. The nerve consists of greater than 1000 unmyelinated axons, mostly less than 1 micron, a very few greater than 1.5 micron in diameter; presumably the efferents recorded from were these larger fibers.