xiv Journal of Comparative Neurology. 



3. This associated movement is always complete; that is, it cor- 

 responds to the execution of a given function. 



3. It is for this reason that, by the excitation of a single root, 

 there come into play muscles of antagonistic action (e. g. extensor 

 and flexor, abductor and adductor), which, however, concur in a 

 combined movement, which will result in the execution of an exceed- 

 ingly complex act, such as leaping, habitual or voluntary, 



4. The fact is worthy of note that by the excitation of roots 

 which correspond and which have an equal or almost equal distribu- 

 tion in the different animals, precisely the same results are not ob- 

 tained, so far as concerns the function. 



5. These results stand in direct relation with the instincts and 

 with the habits of the animal experimented upon. For example, by 

 the excitation of the second sacral root are obtained in the dog wag- 

 ging movements of the tail, movements which the animal executes 

 when it is satisfied or wants to be merry. We may therefore, call it 

 the joy-root. In the cat, however, by excitation of the same root is 

 obtained that attitude of the tail which the animal assumes in mo- 

 ments of anger. Considering now the instincts of the dog and the 

 cat we explam the difference, and thus other examples might be 

 cited. 



6. Nor do the differences concern only diversity of function, 

 but always intensity too, in our opinion m proportion to the instincts 

 and habits of different animals. Thus, for example, the roots which 

 upon excitation give that complex of muscular actions necessary for 

 leaping (IP lumbar in the dog and IV^ lumbar in the cat) are capa- 

 ble of developing, even if excited with a current of equal force, a 

 reaction of very different intensity ; most intense in the cat (an animal 

 especially given to leaping), m.uch less so in the dog. 



7. From this one might be led to think that by hereditary ten- 

 dency and by the habits or exercise of the muscle there may become 

 established functional conditions such as would have for their object 

 to facilitate and render more efficacious the influence of the higher 

 centres ; that moreover here is explained how not only certain instinct- 

 ive acts, but also some others which would ap{)ear to us of a psychic 

 order may be developed even independently of cerebral influence. 



8. The functional distribution of the motor roots has great im- 

 portance from the physiological and clinical point of view. In nor- 

 mal cases this explains to us how the action of the centres is manifested 

 in a manner so rapid and well regulated ; in pathological cases this ex- 

 plains to us how there is possible in some cases the paralysis or the 



