TRANSPLANTATION OF LIMBS IN AMBLYSTOMA 119 



Because of the mosaic nature of the girdle and the subsequent 

 variabiUty in its degree of development in the transplanted 

 position, the motility of the attached appendage is markedly 

 affected b,y developmental deficiencies in this structure. 



2. Shoulder muscles 



In a previous description of the shoulder muscles in larval 

 Amblystoma (Detwiler, '20, p. 123) it was pointed out that of the 

 thirteen shoulder muscles which typically develop, nine only 

 connect the shoulder with the limb. The remaining four serve 

 for anchorage of the shoulder and are of myotomic origin. The 

 muscles connecting the shoulder with the extremity are of somato- 

 pleural origin, as is the limb itself, and their rudiments are local- 

 ized in the tissue included in a typical limb disc (fig. 1). Con- 

 sequently, when the limb rudiment is transplanted, these muscles 

 develop in the heterotopic position (Detwiler, op. cit., pp. 128 

 and 136). Their nerve supply is derived from the brachial plexus, 

 and although all may be differentiated in the heterotopic position, 

 their nerve supply is by no means constant and many cases 

 develop in which these muscles receive defective nerve supply 

 or are completely lacking in innervation — a condition which 

 markedly affects the degree of motility of the transplanted ex- 

 tremity. The incompleteness of their development secondarily 

 accompanying the smaller area for attachment in the reduced gir- 

 dle also serves to hmit the extent of movements of the extremity 

 on the shoulder. 



3. Brachial plexus 



The brachial plexus is normally derived from the ventral rami 

 of the third, fourth, and fifth spinal nerves (fig. 4) . The develop- 

 mental evidence indicates that, under normal conditions, these 

 outgrowing nerves effect connection with the limb rudiment 

 when it occupies its maximal extent (anterior border of the 

 third myotome to the posterior border of the fifth, as shown in 

 figure 1) and that convergence of the nerves and plexus formation 

 results secondarily from the concentration of the limb rudiment 



