THE NERVOUS SYSTEM. 



363 



Fig. 142. 



isolated ; besides these, there are a good many extremely fine, pale 

 fibrils, like the processes of the cells, only more extended, and running 

 in a transverse and longitudinal direction, of which nothing more can 

 be said, as to whether they are nerve-tubes, 

 or are to be referred to the processes of 

 the cells. The gray 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 enlarge- 

 ment ; and lastly, the superior cervical and 

 dorsal portions, in which latter parts its 

 transverse section presents an ellipse, in 

 the cervical region, with the longer dia- 

 meter much developed. It occasionally 

 exhibits, especially in the lumbar region, 

 indications of its being constituted of two 

 halves, inasmuch as the middle appears 

 somewhat clearer, and the lateral portions, 

 owing to the accumulation of fatty gra- 

 nules in the cells, more opaque. 2. With 

 the above-described cells, those of the sub- 

 stantia gelatinosa* pretty nearly agree, only that they are of a faint, 

 yellowish color, 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 numerous 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 inter- 

 nal and an external group (Fig. 112, w, v\ but occurring also in the other 

 portions of the anterior, as well as, though in less number, in the poste- 

 rior horns, whilst they are never met with in the subst. gelatinosa, nor 

 in the gray commissure. All these cells (Fig. 143) are 0*03 0*06 of a 

 line, in size, with nuclei measuring 0*005 0*008 of a line, are fusiform 

 or polygonal, frequently containing brown, pigmentary matter, and fur- 

 nished with from 2 to 9, or even more branched processes, which at 

 their origin are often 0-004-0*005 of a line thick. These processes 

 may be traced to a length of 0-1-0*24 of a line, and ultimately termi- 

 nate in fine fibrils, all of which, scarcely more than 0*0004 of a line thick, 

 are contained within the gray substance. Besides these large and, for 

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

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

 ous, smaller cells, which constitute a complete series between the large cells 



FIG. 142. Cells from the gray central nucleus of the cord in Man, magnified 350 diam. 

 * [The gray matter of the posterior horn. DaC.] 



