Pattern of projections of individual pyramidal tract neurons to the spinal cord of the monkey.

The results suggest : (1) that PT neurons sending axons to motor nuclei innervating distal forelimb muscles branch less than other PT neurons; (2) that a group of PT neurons located close together may influence various species of motoneurons, but that this influence is the strongest on motoneurons of one species; (3) that individual PT neurons terminate only on a small fraction of a given motoneuron group.