FUNCTIONS OF THE SPINAL CORD 893 



the cord in the cells of Clarke's column. Since the superficial grey 

 matter of the vermis is connected by association fibres with the dentate 

 nucleus, and the dentate nucleus by the superior peduncle with the oppo- 

 site cerebral hemisphere, this is also a possible path to the great brain. 



(3) They may reach the antero-lateral ascending tract of the same 

 side through its cells of origin in the spinal grey matter, and, passing 

 through the medulla and pons to the superior peduncle of the cere- 

 bellum, enter the grey matter of the superior worm. 



(4) They may cross the middle line, after entering the cord, through 

 axons or collaterals (p. 872) which run in the anterior and also in the 

 posterior commissure, enter one of the ascending tracts on the other 

 side e.g., the tract of Gowers and continue without further decus- 

 sation up to their central destination. 



(5) They may spread from neuron to neuron in the tangle of the grey 

 matter itself, and pass out again at a different level into one of the 

 white tracts on the same or on the opposite side of the cord. 



Efferent impulses from the brain may travel 



(1) Through the direct or crossed pyramidal tract. 



(2) From one side of the cerebral cortex to the other, and then down 

 the pyramidal tracts corresponding to that side (?). 



(3) From the frontal part of the cerebral cortex, through the anterior 

 limb of the internal capsule to the grey matter in the pons, and thence 

 to the cerebellum by its middle peduncle. 



(4) From the occipital or temporal cortex, in the hinder rim of the 

 internal capsule, to the pontine grey matter, and through the middle 

 peduncle to the cerebellum. From the cerebellum they may possibly 

 pass down to the nucleus of Deiters and thence along the antero-lateral 

 descending tract to the anterior horn of the cord, and indirectly to the 

 periphery. 



All the paths enumerated, as well as others to which it would be 

 tedious to formally refer, and which the ingenuity of the reader may 

 profitably be employed in constructing for himself, from the data 

 already given, are to be looked upon as possible channels for the 

 passage of impulses between the brain and the periphery. But it 

 must be distinctly pointed out that what is certain is in this case 

 much more limited than what is possible. Among the efferent paths 

 it is certain that the pyramidal tracts are conductors of voluntary 

 motor impulses, and that in most individuals the great majority of 

 such impulses decussate in the medulla oblongata, only a small 

 minority in the cord. For a lesion involving the pyramidal tract 

 above the decussation of the pyramids causes paralysis of the oppo- 

 site side of the body, a lesion below the decussation paralysis of the 

 same side. It is certain that when one pyramidal tract has been 

 destroyed, in many animals at least, the resulting paralysis is soon 

 recovered from, at any rate to a great extent, and it is possible that 

 in this case the motor cortex on the side of the lesion has placed itself 

 again in communication with the paralyzed muscles through its 

 commissural connections with the opposite hemisphere. This, 

 however, is not the only alternative, for, as already pointed out, the 

 pyramidal tracts are not the only cortico-spinal paths which can 



