274 Professor E. A. Schdfer [March 20, 



nerves to the muscles. The pyramidal tract fibres do not, however, 

 go directly to the anterior horns of the cord, where the large motor 

 cells are situated, but terminate in what is commonly regarded as the 

 sensory part of the grey matter, viz. the base of the posterior horn. 

 Here they end in fine ramifications, and the nervous impulses which 

 they convey must be carried to the cells of the anterior horn by pro- 

 cesses of other nerve cells, which are found here. In this way the 

 pyramidal tract of fibres connects the cortex of the brain with the 

 motor nerve cells of the spinal cord. The supposition that this is 

 the path which volitional impulses take, in order to pass from the 

 brain to produce movements of the muscles, thus rests upon a broad 

 basis of observation. 



We are met, however, in further considering this question, by the 

 remarkable fact that the pyramidal tracts, well marked as they are 

 in mammals, are entirely absent in all vertebrates below mammals. 

 And yet no one will deny to the fish, the frog, the lizard, and least of 

 all to the bird, the power of exercising volition over its muscles. 

 There must, therefore, exist in these animals some path other than 

 the pyramidal tracts, which, as we have seen, are not represented at 

 all in them, by which the volitional impulses may pass from the 

 cortex of the brain to produce movements of their voluntary muscles. 



The path which connects the brain cortex of the bird with its 

 spinal cord bas been the subject of study by various observers — in 

 this country especially by Professor Boyce and Dr. Warrington — 

 who have made out a distinct and important system of fibres by 

 which, on the one hand, the cerebral cortex is connected with the 

 middle brain, and, on the other hand, the middle brain is connected 

 with the lower centres in the spinal cord and medulla oblongata. 

 The situation of these fibres, which do not form an uninterrupted 

 path as in the case of the pyramidal fibres, but are, as we have seen, 

 interrupted in the middle brain, is not the same as that taken by the 

 pyramidal fibres of mammals. Now since it is certain that mammals 

 have been develojjed from a lower type of vertebrates, it is, to say 

 the least, not improbable that the same tracts as exist in the lower 

 vertebrates would be retained and serve to some extent the same 

 purpose in the mammal. In other words, there may be an alternative 

 path in the mammal by which volitional impulses can be carried 

 from the Ijrain to the spinal cord. 



This supposition is rendered the more probable by an observation, 

 which has been made by more than one experimentalist, to the effect 

 that although a section of the pyramidal tracts in the medulla 

 oblongata or cord does in fact produce voluntary paralysis of the parts 

 of the body below the section, yet, if the animal be kept alive, in the 

 course of a few days or weeks there is considerable recovery from the 

 resulting paralysis, and ultimately volitional movements may be per- 

 formed in much the same manner as before the lesion. It follows 

 from this observation that there must exist in mammals an alternative 

 path for volitional impulses, and it is one of the problems which 1 



