Expcritiiciits in Transplanting Limbs 277 



This interpretation is in accordance with Nussbaum's law that 

 the course of the nerve within the muscle is an index of the direc- 

 tion in which the muscle has grown .^'* In other words, the orig- 

 inal point of contact between nerve and muscle persists as the 

 entrance point of the nerve after growth is completed. 



It is only necessary to suppose that action takes place at very 

 short distances in bringing about first contact between the devel- 

 oping nerve fibers and the cells of the limb bud. Failure on the 

 part of Hensen and the later advocates of his theory to realize this, 

 has led to the great magnification of the difficulties which an out- 

 growing fiber would supposedly encounter in reaching its proper 

 end organ. It is not necessary to imagine, as a number of writers 

 do, that the growing nerve would have to wend its way through 

 a labyrinth of differentiated tissues, extending from the hip to the 

 toes, in order to reach its end organ, but merely that the nerve 

 must grow independently as far as the base of the undifferentiated 

 limb bud, the rest being provided by the development oi the limb 

 itself. The above interpretation calls nothing mysterious, noth- 

 ing hypothetical into play. It is based solely upon known facts 

 and does not postulate the existence of invisible and otherwise 

 unknown structures. It is the only explanation that can be ac- 

 cepted in the present state of our knowledge. Moreover the varia- 

 tions in the distribution of nerves within normal limbs and espec- 

 ially the slight aberrations from the normal which have been 

 noted in the position of some of the nerves in the transplanted 

 limbs meet a ready explanation on this basis. 



The foregoing suggests the consideration ot certain meristic varia- 

 tions in peripheral nerves. ^^ It has long been known, havmg 

 been pointed out especially by Fiirbringer, that the nerve plexus 

 from which a limb is supplied might in two cases have a different 

 metameric origin, and yet the nerves arising from the plexus 

 might be distributed in the same manner in each. Gegenbaur, 

 who, like Fiirbringer, held closely to the theory that muscle and 

 nerve form an inseparable unit, admitted the difficulty of satis- 



'"Nussbaum '94. 



^"This matter was brought up by Dr. McMurrich and Dr. Bardeen during the discussion of my 

 paper at the Toronto Meeting, and has been fully discussed very recently by the latter (Bardeen '07). 



