MICROSCOPICAL STRUCTURE OF SPINAL CORD. 



1031 



line. They may vary from .065- 135 in diameter, unless unusually small, when they 

 measure from .030-. 080 mm. (Kolliker). In a typical example, as represented by 

 one of the ventral radicular cells giving origin to anterior root-libres, from three 

 to ten dendritic processes radiate in various planes, divide dichotomously with 

 decreasing width and finally end in terminal arborizations. In contrast to the robust 

 dendrites beset with spines, the axone is smooth, slender and directly continuous 

 with the axis-cylinder of a root-fibre of a spinal nerve and unbranched, with the 

 exceptions of delicate lateral processes that are given of? almost at right angles. These 

 processes, the collaterals, arise at a variable distance from the cell-body, but usually 

 close to the latter and always before leaving the gray matter. They repeatedly 

 divide and follow a recurrent course within the anterior horn. After appropriate 

 staining the cytoplasm of the nerve-cells exhibits conspicuous accumulations of the 

 deeply staining tigroid substance that lie within the meshes of the reticulum formed by 

 delicate neurofibrillae, 



Fig. 887. 



which not only occupy 

 the cell-body but also 

 extend into the various 

 processes. The fibrillae, 

 however, do not pass 

 beyond the limits of the 

 neurone to which they 

 belong (Retzius). Each 

 nerve-cell possesses a 

 spherical or ellipsoidal 

 ^nucleus, from .010 to 

 .020 mm. in its greatest 

 diameter, which is en- 

 closed by a distinct 

 nuclear membrane and 

 usually contains a single 

 nucleolus, exceptionally 

 two or three. Within 

 the cytoplasm an accu- 

 mulation of brownish- 

 yellow pigment granules 

 is usually present near 

 one pole, often in the 

 vicinity of the implanta- 

 tion cone from which 

 the axone springs. 



In addition to the con- 

 spicuous ventral radicular 

 cells above described, the 

 anterior horn contains 

 other nervous elements, 

 some of which, the com- 

 inissural cells, send their 



axones through the anterior commissure to the opposite half of the cord, while the axones of 

 others, the strand-cells, pass into the columns of white matter of the same, less frequently 

 opposite, side. 



The commissural cells, which with few exceptions occupy the median portion of the 

 anterior horn, resemble in size and contour the radicular cells, but differ from the latter in pos- 

 sessing smaller nuclei. The majority of the dendrites are directed towards the inner part of 

 the ventral cornu, but some pass into the gray commissure and a few end within the adjacent 

 white matter. The axones traverse the anterior white commissure to gain the ventral column 

 > of the opposite side, in which they either divide T-hke into ascending and descending fibres, or 

 undivided turn brainward. 



The strand cells, variable in form and generally smaller than the root-cells, are only 

 sparingly represented in the anterior horn. They are distinguished by the course of their 

 axones, which usually pass to the anterior column of the same side. In some cases, however, 



Nerve-fibres of white matter 



Anterior root-fibres 



Portion of anterior cornu of gray matter, showing multipolar 

 nerve-cells. X 120. 



