ZOOLOGY: S. R. DETWILER 
329 
sixth and seventh nerves, there are no cases which function normally, 
forty eight per cent being totally incapable of movements and fifty one 
per cent showing only greatly impaired movements (table 1 A and 
table 2). 
Inasmuch as there are practically no structural deficiencies within 
the transplanted limb itself, the gradual decrease in the function of the 
limbs, as they are implanted more and more remote from the normal 
region, suggests the following possible factors as conditioning their de- 
gree of function, (a) structural deficiencies in the shoulder girdle, (b) 
deficiencies in the shoulder musculature, (c) the failure of certain of the 
shoulder muscles to receive innervation and (d) the absence of proper 
central neurone connections. 
The shoulder girdle being a mosaic (Detwiler^), there is considerable 
variability in the degree of its development in the transplanted position, 
yet it is found that its development, in general, is no less complete in 
cases where the limb has been removed a considerable distance from 
the normal region than in those where the limb has been removed only a 
short distance. The difference, therefore, in the degree of function of 
the limbs could hardly be a result of this factor alone. Secondly, a 
study of the cross section anatomy of the shoulder region of the trans- 
planted limbs shows that shoulder muscle differentiation does not be- 
come less complete as the limbs are implanted more and more poste- 
riorly. No cases have been found in which there was complete absence 
of any of the muscles which typically develop in the heterotopic position. 
Thirdly, peripheral efferent innervation to the shoulder muscles, 
although somewhat less complete quantitatively in the more posterior 
positions than in cases where the transplanted limb receives segmental 
nerves from all or a part of the normal limb level of the cord, is no less 
developed qualitatively, practically all of the individual muscles re- 
ceiving some nerve fibers. Certainly the degree of defective peripheral 
innervation could hardly account entirely for the very imperfect move- 
ments exhibited by limbs in the series AS5 and AS6 (table 1 A) . 
The remaining factor viz: defective connections within the central 
nervous system appears to be the only one which will adequately account 
for the marked deficiency of function in limbs transplanted so far poste- 
riorly as to be beyond the point where they receive peripheral innervation 
from the normal limb level of the cord. 
Although in normal larvae of this age, the most obvious motor re- 
sponses to various types of peripheral stimulation consist of total swim- 
ming reactions, under certain controlled conditions motor responses 
