io6 THOMPSON YATES LABORATORIES REPORT 
previously* that the overlap of distribution of the constituent fibres of each nerve-root itself is 
even greater than that of the overlapping of contiguous nerve-roots. 
Is the overlapping of the skin-fields of the spinal ganglia paralleled by overlapping of the 
muscular fields of the motor spinal roots P In the hind limb of Macacus I was able to confirm 
Eckhardt's conclusions as to the pluri-segmental innervation of the limb-muscles, although 
Eckhardt's observations had been confined to the hind limb of the frog. In the pelvic limb of 
Macacus I found but one muscle (tensor fasciae femoris) with a nerve supply from a single spinal 
nerve-pair. Tlie other muscles I found to possess a bi-segmental or tri-segmental nerve supply ; a 
fact since confirmed for the same limb in the case of Man by a research by PATERSON.t In the 
upper limb I find similarly that tlie muscles are pluri-segmental, a greater number being tri- 
segmental in the upper limb of Macacus than in the lower limb of that animal. The suhclavius 
muscle seems in some individuals, as I found also tensor fascia femoris and rectus capitis posticiy to be 
uni-segmental, receiving its motor supply sometimes from the Vlth cervical nerve alone : it is in 
so far the only muscle I find uni-segmental in the upper limb. As examples of bi-segmental 
muscles, I find the teres major and anconeus. The palmaris longus, the supinator brevis, the 
supinator longus, anconeus, and the extensor carpi ulnaris, may serve as types of tri-segmental 
muscles, and of quadri-segmental muscles the pronator quadratus, and flexor profundus digitorum 
(in some individuals). Muscles innervated from longer series still are the pectorales, and latissimus 
dorsi. On the other hand, in the intercostal spaces the intercostales externi and interni 
muscles appear, as far as I have yet examined them, to possess a strictly uni-segmental innervation, 
and somewhat similarly in the rectus abdominis, and in the sternalis these muscles have special 
zones for separate distribution of their motor roots. The multi-segmental nature of the nerve- 
supply, in the case of the large muscles at the attached base of the limb (pelvic and shoulder 
muscles), does not necessarily imply much actual overlapping or commingling of the muscular 
territories of the motor roots. I pointed outj that in the case of the lower limb there is much 
' greater overlapping and intermingling of the root districts in the muscles of the foot than 
in those of the thigh.' The same is the case in the arm : the intricacy of the commingling 
in the muscles of the hand is much greater than in those of the shoulder. In the muscles 
of the forearm and hand the manner in which the nerve-fibres of a spinal root are scattered 
through the small muscle-nerves, when examined by the degeneration method, gives a striking 
clue to the great commingling of the root territories in those organs. 
To the question asked at the opening of this paragraph it may therefore be replied that 
there is in the musculature of the limbs, and of certain, though not all of the trunk-musculature, 
an overlapping of motor-root territories quite comparable with that of the cutaneous seiisory 
root-fields ; and the former, like the latter, attains at least as great a development as it attains 
anywhere in tlie distal ends of the limbs. 
What functional significance may he assigned to the overlapping ? Mindful that the overlap 
is maximal in the hand, and that of the structures under consideration here the hand may be 
* 'Phil. Ti-ans.,' B, vol. 184, he. sit. f 'Joiirn. of An;\t. antl Physiol.' 1894, 1895, 
I 'Lumbo-sacral Plexus.' 'Journ. of Physiol.,' vol. 13, 1892. 
