1903.] on the Paths of Volition. 275 



have lately set myself to endeavour to determiue within what part of 

 the medulla oblongata and spinal cord that alternative path runs. 

 The method which I have used has been the production of an arti- 

 ficial lesion or section in a definite jDortion of the medulla oblongata 

 or spinal cord, and the observation of the effects, whether structural 

 or functional, produced by such lesions. 



But before giving you the results of these experiments, I wish to 

 bring before your notice an important tract of nerve fibres which, in 

 conformity with the law that nervous impulses follow degeneration, 

 may, like the pyramidal tract, be regarded as one which carries 

 descending impulses from higher to lower parts. This tract of 

 fibres, which was first described by Lo wen thai, occupies a position in 

 the anterior part of the cord extending somewhat into the lateral 

 region ; it is known as the antero-lateral descending tract, or tract of 

 Lowenthal. The termination of its fibres is in the anterior horn, 

 where their ramifications come into close relationship with the large 

 motor cells which are so characteristic of that part of the grey 

 matter. The origin, on the other hand, of the fibres of the tract in 

 question appears to be twofold. For, if we trace them upwards in 

 sections of the medulla oblongata and pons Varolii, we find that, 

 while a large number of them emanate from a group of cells which 

 are accumulated in grey matter at the side of the medulla oblongata 

 and pons Varolii, and which is known as the nucleus of Deiters, 

 others come from a yet higher part of the brain stem, probably from 

 the part known as the anterior corpora quadrigemina, although their 

 origin has not been quite satisfactorily determined. Each cell of the 

 nucleus of Deiters seuds its nerve fibre towards the middle line, and 

 the fibre there bifurcates, one branch passing upwards towards the 

 mid-brain, where it ends by ramifying amongst the motor cells which 

 give origin to the nerves to the eye muscles ; the other branch turning 

 downwards and passing into the spinal cord, where we see it as one 

 of the fibres of the antero-lateral descending tract, and, as has 

 already been mentioned, terminating amongst the motor cells of the 

 anterior horn. The bundle which these fibres form lies on either 

 side of the middle line ; and from the fact that in the upper portion 

 of its course it is placed in the dorsal or posterior part of the brain- 

 stem, it has come to be known as the posterior longitudinal bundle. 

 But as this posterior longitudinal bundle passes downwards into the 

 spinal cord, it comes to occupy a ventral rather than a dorsal situa- 

 tion, and the name posterior longitudinal bundle now becomes a 

 misnomer, since the fibres lie in the anterior or ventral column. 



Those fibres of the antero-lateral descending tract which are 

 traceable higher up in the brain stem, form a bundle lying ventral 

 to the posterior longitudinal bundle, and, as we have seen, originating 

 apparently in the mid-brain, where they are found crossing over from 

 the opposite side. Their exact origin in the mid-brain is, as already 

 stated, not known, but it is believed that they arise in the grey matter 

 of the corpora quadrigemina, which correspond with the optic lobes 



