CENTRAL NERVOUS SYSTEM. 201 



nerves occurred and sensation and motion returned to the affected parts of 

 the limbs.' It is plain thai by this arrangement the skin and muscles at the 

 periphery must have acquired central connections with the spinal cord very 



different from those normal to them. 



From the experiments of Cunningham, 2 it appears that the results of the 

 cross-suturing of nerve-trunks are about what other facts would lead us to 

 expect. If the trunks concerned control muscles acting in a similar manner, 

 then cross-suturing- produces but slight incoordination as a resull ; where, 

 however, the central trunks normally innervate antagonistic muscles, then 

 incoordination follows and persists. The stimulation of the cerebral cortex at 

 the centre for a given muscle group always causes impulses to pass along the 

 efferent fibres which normally innervate that group, no matter to what muscles 

 these fibres may have been secondarily attached by cross-suturing. More- 

 over, striped muscles which normally exhibit rhythmic contractions lose this 

 function when their innervation is changed by cross-suturing to a nerve-trunk 

 which normally innervates an arhythmic muscle. Thus the central nervous 

 system, in dogs, at least, does not adapt itself to the changed conditions 

 introduced by cross-suturing. 



In a series of investigations, Lam-lev ! has been able to show that when 

 the preganglionic fibres of the thoracic nerves, which send branches to differ- 

 ent groups of cells in the superior cervical ganglion, are allowed to regenerate 

 after section, the several bundles of fibres appear to find and become attached 

 to the cell-group which they normally controlled, since stimulation of the 

 several roots after regeneration gave the reactions which were characteristic 

 for them. However, there is reason to think that the arrangement after 

 regeneration is not exactly the same as that before, and that some fibres have 

 strayed from their original connections. Further, Langley 4 has been able by 

 cross-suturing to establish a connection of the lingual and the vagus nerves 

 respectively with the cervical sympathetic nerve, and so with the superior 

 cervical sympathetic ganglion. Thus we have evidence that fibres other than 

 those normally associated with the ganglion cells can at times form functional 

 connections with them and carry impulses which excite them to their normal 

 functions. This result has an important bearing on the theory of the stimu- 

 lation of one element by another. The reaction following the indirect excita- 

 tion of these cells depends, therefore, on the connections made by their axones, 

 and not on the source of the fibres which excite them. The regeneration 

 thus far described has been that of the axone by the cell-body or perikaryon. 

 Concerning the regeneration of the dendrites, we have no information. 



The possibility of the formation in mammals of new nerve-cells by the 

 division of nerve-elements which are already mature and have been func- 

 tional, has been claimed. 



1 Journal of Physiology, L895, vol. xviii. 



1 Cunningham : American Journal of Physiology, 1898, vol. i. 



3 Langley : Journal of Physiology, 1897, vol. xxii. p. 215. 



4 Langley : Ibid., 1898-9, vol. xxiii. j>. 240. 



