340 



The tractus intermedio-lateralis in Man presents nearly the same 

 appearance as in Mammalia, and contains the same kind of cells. In 

 the lumbar region it is still prominent at the side of the grey sub- 

 stance, but its cells are less numerous than in the dorsal region. In 

 the upper part of the cervical region a similar tract reappears, which 

 is traversed by the roots of the spinal accessory, and those of the 

 spinal nerves. 



In Birds, as in Mammalia, the posterior cornua are united in a, 

 single mass, both in the dorsal region and lower part of the conus me- 

 dullaris ; and the gelatinous substance extends uninterruptedly across 

 from side to side. There are no dark masses corresponding to those 

 of the posterior vesicular columns of mammalia, although numerous 

 cells are scattered through the same space. There are no traces of 

 any distinct tractus intermedio-lateralis. In Reptiles it is only in the 

 conus medullaris that the posterior cornua form a single mass. A 

 distinct stratum of small fusiform cells, in connexion with the fibres 

 of the posterior roots, extends diagonally from the point of each 

 cornu to the transverse commissure. 



In the Ox and Sheep the epithelium of the canal consists, not of 

 cylindrical, but of fusiform cells arranged in close apposition. The 

 fibres proceeding from them are precisely similar in appearance to 

 those of the connective tissue which surrounds the cord, and, like 

 those fibres, they are in connexion at intervals with minute nuclei ; 

 in the filum terminate the author has satisfactorily traced them 

 through the grey substance to the surface of the cord. In ihejllum 

 terminate, where the nerve-cells and nerve-roots entirely disappear, 

 the canal, and consequently the number of epithelium-cells, are much 

 greater than in the cervical or lumbar enlargement, where the nerve- 

 cells and nerve-roots are abundant. These facts are opposed to the 

 statements of those observers who profess to have traced their con- 

 nexion with nerve-cells and nerve-fibres. 



The white columns of the cord are traversed by a network of 

 connective tissue, which abounds with nuclei and small cells pre- 

 cisely similar to those found in the grey substance. 



In the conus medullaris, the author has distinctly seen some of 

 the anterior roots of the nerves form loops around the group of 

 stellate oells, instead of terminating in them. 



