THE NERVOUS SYSTEM. Ill 



to whether they are nerve-tubes, or are to be referred to the pro- 

 cesses of the cells. The grey central substance, taken altogether, 

 is thickest in the lumbar enlargement, and on a transverse 

 section is of a pyriform, scutate, or cordate figure; next to 

 this stands the cervical enlargement; and lastly, the superior 

 cervical and dorsal portions, in which latter parts its trans- 

 verse section presents an ellipse, in the cervical region, with the 

 longer diameter much developed. It occasionally exhibits, 

 especially in the lumbar region, indications of its being con- 

 stituted of two halves, inasmuch as the middle appears some- 

 what clearer, and the lateral portions, owing to the accumula- 

 tion of fatty granules in the cells, more opaque. 2. With the 

 above-described cells, those of the substantia gelatinosa pretty 

 nearly agree, only that they are of a faint yellowish colour, 

 and have 1 — 3 processes and simple nuclei. Besides these 

 cells, the substantia gelatinosa also contains the fasciculi of 

 fibres of the posterior roots which pass through it, and nume- 

 rous other true nerve-fibres (vid. infra). 3. Much developed, 

 well marked nerve-cells, are seated, especially at the apex of 

 the anterior horn, forming an internal and an external group 

 (fig. 112, u, v), but occurring also in the other portions of the 

 anterior, as well as, though in less number, in the posterior 

 horns, whilst they are never met with in the subst. gelatinosa, 

 nor in the grey commissure. All these cells (fig. 143) are 

 0-03 — 0-06"', in size, with nuclei measuring 0-005 — 0-008'", 

 are fusiform or polygonal, frequently containing brown, pig- 

 mentary matter, and furnished with from 2 to 9, or even more 

 branched processes, which at their origin are often 0004 — 

 0-005'" thick. These processes may be traced to a length of 

 0*1 — 0-24'", and ultimately terminate in fine fibrils, all of 

 which, scarcely more than 00004"' thick, are contained within 

 the grey substance. Besides these large and, for the most 

 part, many-rayed cells, there are also found in the grey sub- 

 stance, though more widely scattered among its nerve-fibres, 

 very numerous, smaller cells, which constitute a complete series 

 between the large cells and those of the substantia gelatinosa, 

 and consequently require no further description. 



The nerve-fibres of the grey substance are excessively nume- 

 rous, so much so as to constitute in any case the half of its 

 bulk, if not more, and exhibit the same conditions as those of 



