STKUCTUKE OF THE SPINAL COED. 219 



(neuroglia) which contains a number of nuclei embedded in it. These 

 nuclei belong to branched fibrillated cells (neuroglia-cells), of which 

 the neuroglia is wholly composed. The neuroglia is accumulated in 

 greater amount at the surface of the cord underneath the pia mater 

 (fig. 251), and it extends into the grey matter, of which it may be said 

 to form the basis, and in which it is especially accumulated at the apex 

 (caput) of the posterior cornu (where it forms the substantia gelatinosa of 

 Rolando) and around the central canal. 



The grey matter, besides neuroglia, consists of an interlacement of 

 nerve-fibres and of the branching processes of the nerve-cells which are 

 embedded in it. 



Disposition of the nerve-fibres of the white columns in tracts. 

 The course of the nerve-tracts in the spinal cord, and in other parts of 

 the central nervous system, can best be made out by the method of 

 Flechsig, which consists in the study of sections of the developing 

 cord, for it is found that the formation of medullary substance occurs 

 sooner in some tracts than in others, so that it is easy to make out the 

 distinction between them. Another method consists in investigating 

 the course which is pursued by degenerations of the nerve-fibres in 

 consequence of lesions produced accidentally or purposely. Those 

 tracts in which degeneration of fibres occurs below the lesion are 

 termed "descending" tracts ; those in which it occurs above the lesion 

 are termed "ascending." 



Investigated by these methods, it is found that at the posterior 

 part of the lateral column there is a tract of moderately large fibres, 

 intermingled with smaller fibres, which are found to descend in 

 the lateral column of the spinal cord from the opposite side of the 

 brain, after having crossed at the pyramids of the medulla oblongata 

 (crossed pyramidal tract, fig. 252). The large fibres which lie in the 

 anterior columns next to the anterior median fissure, in the upper 

 part of the cord, belong to a portion of the same tract which has 

 not undergone decussation (direct pyramidal tract). The relatively 

 small fibres of the postero-mesial column belong to a tract, known as the 

 tract of Goll (fig. 252), which consists of fibres derived below from the 

 posterior nerve-roots and postero-lateral column, and ending above in the 

 grey matter of the funiculus gracilis of the medulla oblongata. The 

 postero-lateral column itself (tract of Burdach) is chiefly composed of the 

 fibres of the posterior nerve-roots which run for a short distance in it 

 before entering the postero-mesial column or the grey matter of the cord. 

 The fibres of this tract in the cervical region end in the grey matter of 

 the funiculus cuneatus of the medulla oblongata. In the lateral 

 column there are two other ascending tracts. One of these is only 



