EXAMINATION OF SOME SPINAL NERVES 107 
considered supreme in sentiency of skin and nicety of action, it miglit be imagined that the 
pre-eminence of functional delicacy and of polymeric character of nerve-supply were determinate 
one of the other. That the two features may be correlated I should be the last to deny, but I 
fail to find proof of a casual nexus between them in the sense that one is result of tlie other. 
The overlap is as great in the skin of the back of the hand as it is in the palm, yet touch, as 
tested by localizing power, is far the greater in the latter. It is medius, not index, which possesses 
the triple nerve-root supply, though medius is less sentient than index. The skin of the concha 
is not in Macacus apparently at all specially sentient, yet its sensory innervation is in part as 
regards nerve-pairs a quadruple one. I am more inclined to connect the greater overlap in the 
hand and foot with degree of Lotze's ' local sign,' and with the fact indicated by the arrange- 
ment of the nerve-fields, that they lie approximately in the region of the lateral line of the 
animal as do the nipple and external auditory meatus, a line along which the amount of overlap 
seems to be great, perhaps as a heritage from old ancestral structure. 
Examined by the degeneration method a somewhat greater degree of overlapping of root- 
distribution to the muscles of the limb is evidenced than examination by stimulation reveals. 
The degeneration method by its results explains the cause of the discrepancy between the 
observations by the two methods. The degeneration experiments show that in some muscles 
the number of motor nerve-fibres given by a spinal-root to a muscle is too small to evoke from 
the muscle any contraction at all obvious to inspection. Cases occur where a limb muscle 
receives one, two, three, four, or five motor-fibres from a particular root ; allow to each of tliese 
motor nerve-fibres a dozen muscle-fibres, it is easy to understand that sixty muscle-fibres scattered 
in a muscle consisting of many thousands may cause no perceptible tightening of the tendon ; 
they may simply stretch or compress adjoining inactive and elastic fibres. The degeneration of 
these few fibres I regard as strong evidence of the morphological character of the overlap ; the 
fewness of the fibres is one of the many facts which indicate that the distribution ot the motor- 
roots is arranged on a segmental plan in accordance with the terms of a bequest dating back to a 
time when the present environment of the limb, especially in its Mammalian form, had no 
preponderant weight in the shaping thereof. As regards functional value, this ciiaracter ot the 
Mammalian limb is on a par with details of structure which are not specific, and, therefore, with 
other details of structure outside those immediately acquired by the species, not to be considered 
as of necessity of present functional importance. The functional use of the contribution ot one 
or two nerve-fibres to a muscle requiring hundreds is difficult to see ; the probability of the 
occurrence of such poverty-stricken contributions is, on the view of the morphological necessity 
of the ray-arrangement of the limb mvisculature, so high as to be only what might Iiave been 
expected from theoretical considerations. The fact that certain of the motor roots ot tlie limb 
contribute fibres to the innervation of certain muscles in such scanty number as to be ineffective 
for movement, is a further argument for the morphological rather than functional character of the 
motor-root distribution in the Mammalian limb. A number of motor-fibres, too small to evoke 
appreciable movement in a muscle when excited electrically, will liardly be effective for movement 
under the action of the will. 
