282 Journal of Comparative Neurology. 



In Amblystoma, sensory neurones of the second spinal 

 nerve enter the ventral ramus and are distributed to the skin of 

 the pectoral region. Druner recognizes such neurones in the 

 corresponding nerve of Salamandra and Triton, but gives no 

 account of their distribution. It would have been instructive 

 had he given, also, the distribution of the sensory neurones 

 which no doubt pass into the ventral ramus of the third spinal 

 nerve in Proteus and Menobranchus which have no ganglion on 

 the second spinal nerve, for it is probable that these neurones 

 have advanced into the territory which typically belonged to 

 the second spinal nerve. If this supposition should prove cor- 

 rect it would be plain evidence in favor of the theory of 

 "usurpation of nerves" (Herrick, '99, p. 415) by which I 

 have explained the peculiarities of the amphibian r. alveolaris 

 VII and r. mandibularis VII. Indeed, it is obvious that in 

 adult Amblystoma there is typically one segment, and in Pro- 

 teus or Menobranchus two adjacent segments, without a spinal 

 ganglion, and it is impossible to explain the cutaneous innerva- 

 tion of these segments without the presence of neurones from 

 other segments. It seems necessary, therefore, to assume that 

 one nerve, in the course of time, may usurp the function of the 

 nerve of an adjacent body segment. 



The branchial ramus of the second spinal nerve to the 

 third external gill, which I have described for Amblystoma, has 

 not been observed in other Amphibia. 



VI. Conclusions. 



1. The two elements of the olfactory nerve of Ambly- 

 stoma represent the two roots of the nerve in Gymnophiona 

 and Triton. 



2. Because of the great variation which occurs in the 

 peripheral relation of the eye-muscle nerves, great caution 

 must be observed in dealing with the morphological significance 

 of these relations. 



