EXAMINATION OF SOME SPINAL NERVES 117 
the very posterior segmental nerve-supply recorded in my table, is probably explicable by its lying 
so distally in the forearm. A difficulty is, however, the superficial part of the intrinsic thumb 
muscles, which receives a, segmentally-considered, less posterior motor innervation than the deeper 
intrinsic thumb muscles. The anterior position of the thumb as compared with other digits may 
explain this, although the difficulty does appear to me considerable. In the leg, as I showed, 
the deep flexor of the toes is supplied by nerve-roots segmentally anterior to those supplying the 
soleus and gastrocnemius. The arrangement is not a different one in the two limbs ; I believe it 
to be essentially the same ; but it is more clearly expressed in the lower than in tlie upper ; it was 
with the upper only that the work of Herringham dealt, and it is in that I admit that the 
arrangement which I consider to hold good, to the exclusion of the one formulated by 
Herringham, is the less clearly to be traced. 
I have pointed out in a previous paper* that the spinal region of outflow of motor fibres is 
for the hip joint longer than for the knee-joint, for the knee-joint longer than for the ankle-joint. 
The segmental length of the region of outflow of motor fibres for a joint may be said, in the case 
of the hind limb, to be great in proportion as the joint lies proximal, less in proportion as the joint 
lies distal in the limb. Just as this rule is broadly true of the hind limb, so does it apply also to 
the fore-limb.t The outflow of motor fibres to the shoulder embraces six consecutive spinal 
nerve-roots, that to the elbow five, that to the wrist five, and that to the finger-joints four (if wc 
omit the occasional supply from Vlth to extensor metac. and flex. long, pollicis, and the small 
contribution from the same root to the extensor digitorum). But if each of the main movements 
of the joints be considered individually, it is seen tliat the region of representation in the spinal 
roots is at least as long in the case of the distal joints of the limb as it is in the proximal, and the 
long region of motor outflow in the case of the large proximal joints is seen to be due — as I have 
already pointed out for the lower limb — to the motor representation of tlie main movements of 
each joint being more separated (e.g., flexion more separated from extension) one from another in 
segmental position in the case of the proximal joints than in that of the distal. For example, for 
the movements of flexion and extension at elbow-joint, flexion efFerents leave the cord from the 
5th, 6th, and 7th, and to a small extent also from the 8th segment ; extension efFerents, on the 
other hand, from the 7th, 8th, and 6th, and to a small extent from the 9th segment. The 
movements at the finger joints are, on the contrary, segmentally situated as follows : when judged 
by motor outflow from cord ; flexion efFerents from lOth, 9th, 8th, and to a less extent from 7th 
segments, extension efFerents from 7th, 8th, 9th, and to a less extent from loth segments, and still 
less from 6th segment. One might express the difFerence by saying that lengthwise along the 
cord the motor-nerve-cell groups for flexion and extension overlap each other very slight/]! in the 
case of the proximal joints, but very largely for the distal joints. In the case of the elbow, the 
extreme limits of overlap of flexion and extension motor-neuron groups embrace three spinal 
segments, but the overlap lies mainly in one segment, namely, Vllth cervical. In the case of tlic 
digits, the extreme limits of overlap of flexion and extension motor-nerve-cell groups embrace five 
« 'Journ. of Physiol.,' 1S92, vol. 13, p. 74b. 
f See the 'Conspectus,' opposite p. 114. 
