276 Professor E. A. Schdfer [March 20, 



of birds. Now it is precisely the optic lobes in birds which furnish 

 an important intermediate station for the main tract of fibres con- 

 necting the cerebral hemisphere with the lower nerve centres, and on 

 this ground alone it is extremely probable that the bundle of fibres 

 which we are now discussing, and which is known as the ventral 

 longitudinal bundle, is a part of the alternative path by which voli- 

 tional impulses may pass from the cerebral cortex to the spinal cord. 

 Moreover, in mammals also, as well as in birds, there exists a system 

 of fibres which is known to connect the cerebral cortex with the 

 middle brain, and which has quite recently been the subject of a 

 special investigation by Dr. Beevor and Sir Victor Horsley. 



I now come to the results of my own experiments. I have, in the 

 first place, been able to confirm the statement that section of one or 

 both of the pyramids of the medulla oblongata, involving as it does 

 section of all the fibres of the pyramidal tract of one or both sides, 

 produces paralysis below the lesion, which, although complete at first, 

 is not lasting. This point settled, the next object was to determine, 

 what, under these circumstances, is the alternative path along which 

 volitional impulses from the brain to the anterior horn now pass ; and 

 in order to do this I have, both as a primary lesion and also as a 

 lesion secondary to the injury of the pyramidal tract, cut the antero- 

 lateral descending tract upon one or both sides of the cord. For, 

 from the anatomical relations of these tracts, and especially the close 

 connection which they have with the motor cells of the cord, it 

 seemed most probable that the alternative volitional path would pass 

 along them. This supposition appears to be confirmed as the result 

 of the experiment, for, in all cases in which the antero-lateral de- 

 scending tracts are cut, there is very pronounced voluntary paralysis 

 in the parts of the cord below the section. 



It might be thought that this experiment definitely settles the 

 point, and that we may conclude as a result of it that there are two 

 paths for volitional impulses, the one following the pyramidal tract 

 and the other following the antero-lateral descending tracts. The 

 matter, however, is not so simple as it seems ; and in order to illustrate 

 this I have only to bring before your notice a remarkable experiment 

 which was performed by Dr. Mott and Professor Sherrington, which is 

 itself a modification of a much older experiment of Sir Charles Bell. 

 Sir Charles Bell found after he had cut the sensory nerve of the face 

 in an ass, that the result of the section was not only to abolish sensa- 

 tion on that side of the face, but also to abolish voluntary action of 

 the facial muscles. Mott and Sherrington extended this observation 

 by cutting in a monkey the posterior roots of all the spinal nerves 

 which supply fibres to one arm. These posterior roots contain, as is 

 well known, only sensory fibres, and yet the result of their section was 

 the production of just as complete a paralysis for voluntary motion as 

 if the anterior roots, the fibres of which directly conduct impulses for 

 volition, were themselves severed. Mott and Sherrington were in- 

 clined to regard their experiment as indicating that volitional impulses 



