158 S. R. DETWILER 



SimiMARY 



1. Shifting the position of the fore-Hmb rudiment a given num- 

 ber of body segments anterior or caudal to its normal site, does 

 not effect to the same extent a corresponding shifting of the seg- 

 mental nerve contribution to the brachial plexus. There is a 

 marked tendency for transplanted limbs to receive innervation 

 from the normal limb level of the cord (table 2 and figs. 4, 5, 16, 

 and 18). 



2. The number of segments occupied by a transplanted limb 

 does not determine the number of segmental nerves contributing 

 to its plexus. 



3. When the fore-limb rudiment is transplanted from two to 

 three segments anterior to the normal position, the distal portions 

 of the normal limb nerves are found to grow anteriorly the dis- 

 tance of several segments to effect functional connection with the 

 heterotopic appendage. The proximal portions of the nerve 

 follow a normal pathway (fig. 16, cf. fig. 4). In effecting connec- 

 tions with the limb, the nerves apparently grow anteriorly against 

 the mechanical opposition of the developing myotomes, which 

 tends to direct them caudally. 



4. From the results of the present limb experiments, in addition 

 to those previously pubHshed (Detwiler, '20), evidence has 

 accumulated which strongly suggests that there exists between 

 the limb and its normal nerves a developmental relationship 

 which is more intimate in character than any developmental 

 association between these same nerves and other structures. 

 The contention is thus supported that mechanical influences, 

 although governing in large measure the character of nerve 

 pathways, do not reveal the mechanism by which proper connec- 

 tions are made at the periphery. 



5. The function of transplanted limbs is conditioned by four 

 main factors: 1) structural incompleteness of the shoulder- 

 girdle; 2) defective development of the limb and the shoulder 

 muscles; 3) defective peripheral innervation, and, 4) defective 

 connections within the central nervous system. 



6. The gradual loss of function in limbs as they are trans- 

 planted farther and farther away from the normal situation is 



