154 S. R. DETWILER 
vertebral foramina they begin to elongate posteriorly and in the 
general direction of the transplanted limb. It could easily be 
. assumed that these nerves, not finding a sufficient number of 
muscles to accommodate the sum total of their fibers as they 
grow posteriorly, would so continue to grow until the limb muscles 
were reached and total connections were made. However, in 
the absence of any directing influence of the transplanted limb 
on these nerves, there is no apparent reason to expect that they 
should enter the imb. Further, why should not the outgrowing 
nerves corresponding to the segments occupied by the trans- 
planted limb effect its sole innervation? For example, if a limb 
is transplanted so that its position corresponds to the eighth, 
ninth, and tenth segments, the outgrowing nerves corresponding 
to these same segments are closer to the limb rudiment than are 
those coming from segments of the cord situated anterior to the - 
limb, yet those nerves situated anterior to the position of the 
displaced rudiment are the ones which contribute the main bulk 
of the nerve supply. Only by recognizing the presence of a 
guiding influence and a positive reaction of the nerves toward 
it, can the nerve supply to transplanted limbs be adequately 
explained at present. By the use of such an hypothesis we can 
explain why the nerves of the normal limb level, especially the 
fourth and fifth, will grow a longer distance posteriorly to effect 
limb innervation than those from more posterior segments. 
Such an explanation can only be made by assuming that the 
positivity toward this influence is greater at this level of the cord. 
The facts as shown in table 2 would seem to agree with such an 
assumption, for this table shows that the farther away from the 
normal level the limbs are transplanted, the less the tendency 
to be innervated from segments situated anterior to the position 
of the limb rudiment and the greater the tendency to be inner- 
vated by segments corresponding to the position occupied by 
the limb. The presence of such an influence as seems to be 
exerted by the autoplastic limbs may be an expression of a 
mechanism whereby the anterior limbs, when set back a number 
of segments, can function codrdinately with the opposite intact 
limb, for we have already seen that limbs transplanted poste- 
