EXAMINATION OF SOME SPINAL NERVES 97 
extremity, and is always quite small in extent. If, therefore, in a series of experiments of the 
kind under description, the field of the Vllth cervical root is found to include in the left hand 
portions of skin included by the field of the 1st thoracic in the right hand, a triple overlap of the 
fields of the Vlllth cervical, Vllth cervical, and 1st thoracic may be taken to be proven to exist 
there. And such is actually the case. The triangular area of skin on the dorsum and palm of 
the hand shown in figures between the two dotted lines marked 7 and i, is an area of triple root 
supply. It is notable that tlie area increases in width as followed from the wrist to the fingers, 
including in the latter position the whole of the medius and tlie adjacent sides of index and 
annulus. The area lies along the dorsum and palm, somewhat, but not much, towards the ulnar 
side of the mid-line of the hand. 
Again, the pinna of the ear is in part a region of triple overlap, namely, in the fossa 
triangularis, tragus, opening of the meatus and part of the fossa of the antihelix. In this latter 
portion it is probably a region of quadruple overlap, the curious little skin-field of the vagus 
coming into combination with the fields of the cranial Vth, and of the Ilnd and IlIrd cervical 
nerves. 
On the other hand, in certain regions, e.g., along the back of the trunk about midway 
between the mid-dorsal and mid-lateral lines of the body, I think the amount of overlap of the 
root-fields in the skin of the Monkey is not so great as to amount to a full half of the contiguous 
field of each of the two consecutive nerve-roots. This point is, however, a difficult one to feel 
satisfied upon ; experiments upon animals are really hardly suitable for deciding it ; chiefly because 
in this region the degree of sensitiveness of the skin is comparatively low, and to obtain clear 
evidence of sensation, and therefore to have distinct knowledge of the extreme boundary of the 
field of remaining assthesia, is often by no means easy. The observations on which I rely do, 
nevertheless, distinctly indicate that in the dorsal region above mentioned, the amount of overlap 
of the consecutive skin-fields is less than, for instance, in the hand. It is therefore safe to say 
that amount of overlapping of the fields of distribution of adjacent sensory spinal-roots is not 
equally great in all regions of the body. 
Is the amount of overlapping of the fields of the spinal nerve-roots greater or less than that of the 
territories of peripheral nerve-trunks F That the skin-fields of neighbouring peripheral nerve-trunks 
do overlap is generally recognized, but very little experimental evidence exists on the subject. I 
have therefore made some observations on the foot and hand of Macacus rhesus and sinicus. I find 
the results much less open to individual variation than in the experiments upon the spinal nerve- 
roots innervating the same region. The figures illustrate the areas of anaesthesia obtained by 
section of the musculo-cutaneous and anterior tibial nerves, combined on the one side with section 
of the both plantar nerves, on the other with section of the external plantar only. 
It will be noted that the field of the internal saphenous nerve in the Monkey reaches 
along the tibial and dorsal aspect of the hallux very nearly to the tip of that digit. This is in 
agreement with the fact that, as shown in my previous paper, the Vth lumbar of Macacus rhesus 
has a skin-field which runs down upon that aspect of the hallux. 
In Macacus the nerve seems to descend further along the hallux than it does in Man. 
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