In an article "On the Anatomical Constitution of Nerves of Skeletal Muscles." (Journal of Physiology, Vol. 17, pp. 211-258.) Sherrington reports a study of sensory and motor fibres supplying different muscles. He says: "Taking the whole series together, the average proportion of the afferent fibres to the total myelinate fibres in the nerves of the muscles examined proves to be a little less than a half (49%). The proportion of afferent fibres to the total myelinate fibres ranges from a little more than a third in some muscular nerves to a full half in others." (p. 229.) "In the nerves to some muscles the afferent fibres are as numerous as the efferent. It is probable that the very largest cells in the spinal ganglia belong to some of the nerve-fibres of the muscle spindles. Probably in every spinal ganglion a number of the nervecells belong to the sense organs of muscles." (The Spinal Animal. Medico-Chirurgical Translations, Vol. LXXXII, p.
Dunn caused all the motor nerves to the legs of a frog to degenerate and "found that there remained an ample supply of medullated fibres to the muscles. These represent from 15 to 30 per cent, of the fibres going to the muscles."
Assuming that the relative motor and sensory nerve supply to the voluntary muscles of the guinea pig and white rat is approximately the same as it is for the animals studied by Sherrington and Dunn, we have in their results an excellent neurological basis for the psychological results obtained by Small and Watson with the rat and Allen with the guinea pig. (Watson, Mon. Sup., Psy. Rev., May, 1907. Small, Am. J. Psy., Vol. 12, pp. 206-239. Allen, Journal Comp. Neur. and Psy., Vol. 14, No. 4.)
Both Small and Watson, especially the latter, found that kinaesthetic processes play a highly important, if not a preponderating r61e in the controlled movements of the rat when learning to run the maze. Allen found that in case of the guinea pig "vision is an important element" but that the "labyrinth is not learned solely, or even largely, in terms of tactual sensations." Her conclusion is that "kinaesthetic sensations are of great importance in the recollection of a path." (Op. cit., pp. 330, 336 and 337.) Yerkes working with the frog came to practically the same conclusions, finding that "beyond question vision and the direction of turning were all important factors in the establishment of the habit." (Harvard Psy. Stud., I, p. 579.)
In connection with what Allen finds to be true with the guinea pig, it is interesting to recall that frequently in human cases of locomotor ataxia the cutaneous sensibility escapes injury while the muscular sense always suffers more or less and
