THE SPINAL CORD. 



661 



and the encephalic centres, yet there are difficulties, in such a view of the case, 

 which must be taken into account in our physiological consideration of it ( 700). 

 697. The " gray matter" of the Spinal Cord is readily brought into view by 

 making transverse sections in different parts : and although its distribution is 

 by no means uniform, yet on the whole it may be described as constituting 

 (when thus exposed) two somewhat crescent-shaped masses (Fig. 174), whose 

 convexities are turned towards each other, and are connected by the gray com- 

 missure, whilst their cornua are directed towards the surface of the cord ; the 

 posterior peak on either side reaching the posterior lateral furrow, whilst the 

 anterior, though the larger cornu, does not approach quite so near to the surface. 

 This gray matter, however, is by no means uniform in its texture throughout. 

 A considerable part of the posterior cornua is destitute of vesicular or gangli- 

 onic corpuscles, and is known under the name of substantia gelatinosa (</) j it 

 has been lately shown by Mr. J. L. Clarke, however, that a tract of vesicular 

 matter does exist on either side (e), in intimate connection with the posterior 

 roots of the nerves, and that this may be traced continuously from the lower 

 extremity of the spinal cord to the medulla oblongata where it terminates, and 

 that it increases in size in the lumbar and cervical enlargements. The gray 

 matter of the anterior cornua, which has been distinguished as the substantia 

 spongiosa, contains a large amount of vesicular structure (d, cT), the number of 



Transverse section of Human Spinal Oord, through the middle of the lumbar enlargement, showing on the 

 right side the course of the nerve-roots, and on the left the position of the principal tracts of vesicular mat- 

 ter : A, A, anterior columns ; p, P, posterior columns ; L, L, portion of lateral columns ; a, anterior median 

 fissure ; p, posterior median fissure ; b, b, b, b, anterior roots of spinal nerves ; c, c, posterior roots ; d, d, tracts 

 of vesicular matter in anterior column ; e, tracts of vesicular matter in posterior column ; f, spinal canal ; g, 

 substantia gelatinosa. 



vesicles being constantly in direct proportion to the size of the nerve-roots in 

 connection with it. The vesicles are of the stellate character, each having 

 several prolongations which seem to unite with those of other vesicles; and 



