270 



NORMAL HISTOLOGY. 



sented in the anterior cornu. Their axones usually pass to the anterior column of the 

 same side, but sometimes an axone divides, one fibre crossing by way of the anterior 

 white commissure to the opposite anterior column, while the other passes to the col- 

 umn of the same side. 



Although the nerve-cells of the anterior cornu are widely scattered, they are not 

 uniformly distributed through the gray matter, but are collected into more or less 

 definite groups that recur in consecutive sections. It is evident, therefore, that the 

 cell-groups are not limited to a single plane, but are continuous as cell-columns for 

 longer or shorter stretches within the gray matter. The grouping of the nerve -cells 







Accessory dorso- 

 lateral group 



Ventro-lateral group 



Median group 

 FIG. 316. Half-section of lower cervical cord , showing grouping of the nerve-cells. X 20. 



of the anterior cornu includes two general collections, a mesial group, containing: 

 many commissural cells, and a lateral group, composed chiefly of ventral radicular 

 cells. These collections, moreover, vary in extent and definition in different parts of 

 the cord, and, where well marked, are often made up of more than a single aggrega- 

 tion of cells. This is particularly true of the lateral collection, in which an anterior 

 and a posterior subdivision are recognized as the ventro-lateral and the dor so- lateral 

 group (Fig. 316). The mesial collection, situated within the ventral angle of the horn, 

 is sometimes, but much less clearly, divisible into a ventro-mesial and a dorso-mesial 

 group, the latter being variable and at many levels wanting. 



The nerve-cells of the posterior cornu are neither as large nor as 

 regularly disposed as the anterior horn cells. Only in one locality, along 

 the median border of the base of the posterior cornu, are they collected into 

 a distinct tract the column of Clarke; elsewhere, they are scattered without 

 order throughout the gray matter of the dorsal horn. In a general way, 



