23 NUCLEI IN THE NERVE CELLS. 



Between January and July, 1880, comparative measurements of 

 nuclei in other species were made, and it was found that, in the gopher 

 turtle, land species the nuclei in the large nerve cells of the spinal 

 cord were larger, in the cervical, than in the lumbar region. The pow- 

 er of the muscles of the anterior limbs, in this species, considerably ex- 

 ceeds that of the posterior limbs. 



Measurements of the nuclei in the cells related to the cranial motor 

 nerves, in frogs, alligators, lizards and turtles, gave still stronger evi- 

 dence of the existence of a law, the wording of which, as first formu- 

 lated, was then changed so as to make it more comprehensive, and to 

 read : The nuclei of the so-called motor cells of the central nervous system, 

 have, in the same individual, average diameters which are proportional to 

 tfie power developed in the related muscles. 



No valid objection to this proposition has yet appeared from any 

 quarter, while verifications have steadily accumulated. 



In stating, at first, what seemed to be true in regard to the spinal 

 cord of the frog and gopher turtle, the word extremities was used in- 

 stead of the word muscles. The latter is of wider application and has 

 since been thought to agree with the facts observed, in another interest- 

 ing particular. For example : In the green turtle, the anterior extrem- 

 ities are much more complex in their functions, and are supplied with 

 more muscles than the posterior extremities ; while the separate muscles 

 appear no larger than the corresponding ones of the posterior extremities. 

 The same thing is true of the bat ; and in both of these animals, there 

 is little or no difference between the dimensions of the cervical and lum- 

 bar nuclei, although in the cervical region of both animals, the large 

 cells are several times more abundant. 



The most striking confirmations of the above rule are to be found 

 in the cells of origin of the cranial motor nerves, in all the species so far 



