In a study of first-order mechanoreceptive afferent fibers innervating the raccoon's glabrous forepaw skin, two types of units, rapidly and slowly adapting (RA and SA), were distinguished, both belonging to the group II class. General characteristics of the two types have been described, as well as the nature of their response to precisely controlled mechanical stimuli. Average rate of responding of both to mechanical stimuli having constant velocity is a power function of velocity. Vibratory tuning points were in the range of 7–10 Hz for the SA and 20–100 Hz for the RA. The M-r papillae are slowly adapting and exquisitely sensitive mechanoreceptors sitting at the base of each digital rete ridge. The rete ridge is, in turn, mechanically coupled to the grossly observable epidermal domes on the skin surface. Local amplification is evident from the multiple neurites innervating each M-r papilla. Overlapping receptive fields are absent anatomically and physiologically. The discrete and small (<1 mm in diameter) receptive fields permit anatomical localization of the receptor.Information on transient deformation is coded by the dermal simple corpuscles which are rapidly adapting. These also exhibit discrete, small, nonoverlapping receptive fields permitting anatomical localization of the receptor. Their anatomical variability deserves further study.