Johnston, The Brain of Petroniyzon. 63 



traced the fibers from their roots to the central endings. As I 

 have described in detail for Acipenser ('01 c, p. 26-27 of the 

 reprint) both direct root fibers and arcuate fibers pass through 

 the narrow neck mentioned above. The same thing is probably 

 triie in Mustelus, since the correspondence in other particulars 

 is so complete. Houser has failed to follow the root fibers 

 through his general cutaneous nucleus. Aside from this differ- 

 ence in our results, there is a very great improbability in Hou- 

 ser's description, arising from the relative size of the parts con- 

 cerned. Houser assigns the whole of his very large general 

 cutaneous nucleus to a part of the trigeminus, the spinal V por- 

 tion of that nerve going to the enlarged anterior end of the 

 dorsal horn; while only the much smaller tuberculum acusticum 

 serves as the place of ending of the great acustico-lateral sys- 

 tem, except those fibers which go to the cerebellum. Even 

 these latter pass through the acusticum. In other fishes both 

 the V and the acustico-lateral fibers pass through or end in the 

 body which he calls the general cutaneous nucleus. 



These criticisms, however, do not in any way discredit the 

 admirably clear and accurate account of the nerve elements in 

 these and other parts of the brain. There is a remarkable 

 agreement in the structure of the cutaneous sensory centers in 

 Mustelus, Acipenser, and Petromyzon and the results of Hou- 

 ser's work give in general a very strong confimation of my con- 

 clusions on the origin of the acusticum and cerebellum and 

 their relation to the dorsal horn of the cord. 



The use of the term gcne?'al cutaneous nucleus, suggested 

 by Houser, does not seem to the writer admissable, for the 

 reason that the general cutaneous fibers do not end in any one 

 nucleus or set of nuclei to the exclusion of other fibers. The 

 fibers of the trigeminus in fishes have endings in the nucleus 

 funiculi, nucleus trigemini spinalis, acusticum, and cerebellum. 

 The only one of these nuclei which is exclusively general cuta- 

 neous is the nucleus trigemini spinalis, but since this receives 

 only the smaller part of the general cutaneous fibers it seems 

 best to keep the term which indicates its relation to the spinal 

 V tract. - 



