101 

 of the spinal corl, exteniini^ t'or^ari. It h'ii come to be ne- 

 glected entirely in recent years o/»inf5 to the prevalent view 

 that it naerely represents a coagulation of the cerebrospinal 

 fluid. Sargent (1900) demonstratei that such a vie^r is erro- 

 neous, that Reissner's fibre is a real structure, with a per- 

 fectly definite character and distribution, and, f urthemore, 

 that it is found in all classes of vertebrates, always extend- 

 ing from the postsrior end of the canalis centralis to the an- 

 terior end of the aqueduct of Sylvius. He nas also sho^a (1901) 

 that the fibre represents, in the main, the closely fused ax- 

 ones of the cells of the roof-nucleus. The great number of 

 neurones comprising the anterior field of the roof-nucleus 

 send their axones into the aqueduct of Sylvius, as noted a- 

 bove, whence they pass backward as Heissner's fibre through 

 the extent of the fourth ventricle and the central canal of 

 the spinal cord. Pine processes are given off to the nervous 

 matter of the cord as the fibre proceeds. 



An interpretation of tne roof-nucleus and of Seissner's 

 fibre arising from it may now be attempted. In the next to the 

 last paragraph, a nexus was traced between the fibres of the stra- 

 tum medullare profundum and the neurones of the roof-nucleus. 

 There are here, it is evident, the elements of a tract through 

 which quite direct connections may be established between the 

 somatic motor neurones of the spinal cord and certain sensory 

 impressions, visual and olfactory, at least. The classes of 

 impressions noted are carried through the stratum melullare 



