2 20 



NERVOUS SYSTEM. 



[sect. III. 



c 



- 



,f 



Transverse section of human spinal cord, close to the 

 third and fourth cervical nerves ; magnified ten diameters 

 (from Stilling) f. Posterior columns, ii. Gelatinous sub- 

 stance of the posterior horn. k. Posterior root. I. Sup- 

 posed anterior roots, a. Anterior fissure, c. Posterior 

 fissure, b. Gray commissure, in which a canal is contained, 

 which, according to this writer, extends through the 

 length of the cord. g. Anterior horn of gray matter con- 

 taining caudate vesicles, e. Antero-lateral column (from 

 k to «). v 



spread from it into the posterior grey horns, and towards the 

 lateral and anterior columns. The anterior commissure, whose 

 rig. 93. thickness is in a great mea- 



sure proportionate to that of 

 the motor roots, and whose 

 breadth is dependent upon 

 that of the spinal marrow, 

 is, accordingly, in part a 

 real decussation of the an- 

 terior columns. 



The roots of the spinal 

 nerves (fig. 93), without as- 

 sociating at all with the lon- 

 gitudinal fibres, pass between 

 them horizontally, or in a 

 slightly ascending direction, 

 from the sulcus lateralis an- 

 terior and posterior, in order 

 to dip into the anterior and 

 posterior grey laminee, where 

 we shall meet with them 

 again. Their nerve-tubes possess, as they pass into the cord , all the 

 characters of central fibres, and at first measure, in the sensitive 

 roots, 0-004"' to 0-006'", in the motory up to 0-008"', but visibly 

 become narrower and narrower, so that finally the former pass into 

 the grey substance with a diameter scarcely more than 0-0012"' 

 to 0-0028"', the latter with a diameter generally not more than 

 0-004"'. 



In the grey substance, the nerve-cells and the nerve-tubes are 

 deserving of special consideration. The former occur in various 

 forms; but all agree in the circumstance, that they invariably 

 possess several processes, which finally, ramifying, run out into very 

 fine pale fibrils, like the finest central fibres of the nerve-tubes. 

 At the apex of the anterior horn especially, they are well- developed . 

 large nerve- cells, forming an inner and an outer group (fig. 93 g); 

 they also occur in the other parts of the anterior horn, and also, 

 although less numerously, in the posterior horn, in which, between 

 the two enlargements, a part of them forms a very remarkable 

 group, at the outer side of the apex of the posterior fasciculi 

 {Clarke's posterior vesicular columns), but never in the sub- 

 stantia gelatinosa and the grey commissure. All these cells are 

 0-03'" to 0-06'" in size, fusiform or polygonal, frequently brown- 

 pigmented, with nuclei of O'oos'" to 0-008'", and with 2 to 9, or even 



