Conduction velocity in proximal and distal portions of forelimb axons in the baboon.

1. Peripheral nerves of the baboon's forelimb were stimulated at different sites, and the latencies of antidromic action potentials were measured in intracellular records from forelimb motoneurones.2. The conduction velocity of single motor axons was slower in the brachial plexus than in the nerves of the arm and forearm. This proximal slowing of conduction velocity was more marked for rapidly conducting axons than for the more slowly conducting ones.3. Gross recordings from dorsal and ventral roots showed that the conduction velocity was slower in the brachial plexus than in the arm for fast afferent as well as efferent nerve fibres.4. The proximal slowing of conduction velocity was shown to be due neither to errors of measurement nor to proximo-distal differences of temperature.