Innervation density of mechanoreceptive fibres supplying glabrous skin of the monkey's index finger.

1. The innervation densities of mechanoreceptive fibres supplying the ridged glabrous skin of the middle and terminal phalanges of the monkey's (Macaca nemestrina) index finger were estimated using a combination of histological and neurophysiological procedures. 2. This estimate was based on (a) a count of the total number of A beta myelinated fibres in the palmar digital nerve at the level of the proximal phalanx, (b) the demonstration that the majority of A beta fibres in the monkey's palmar digital nerve are mechanoreceptive afferents, (c) the estimation, based on a sample of 398 fibres, of the fractions of rapidly adapting, slowly adapting and Pacinian mechanoreceptive fibres in the palmar digital nerve, and (d) the estimation of the area of glabrous skin innervated by the palmar digital nerve. 3. The estimated innervation density of the finger pad and the skin of the middle phalanx were: rapidly adapting fibres, 178 and 80/cm2; slowly adapting fibres, 134 and 46/cm2; and Pacinian fibres, 13/cm2 for both phalanges.