THE SPINAL CORD I7 



of the antero-lateral column in the division of it known as Cowers' tract (h). These are sup- 

 posed to be sensory in function and to transmit sensations of pain and temperature. There 

 are other cells in this median region of the gray matter which send their neuraxons across 

 the median line through one of the commissures to the opposite side of the cord (g). These 

 are known as commissural cells, and serve to transmit sensory impulses across the cord. Many 

 of the cells of this median gray matter are concerned in the reception and transmission of 

 sensations received through the posterior nerve roots. 



The gray commissure uniting the two halves of the gray matter of the cord has in its 

 centre the central canal. This is seen in Plate II. to be lined with cylindrical epithelium. 

 The white commissure lies in front of the gray and contains many decussating fibres. 



The entrance of the posterior nerve roots is well shown in Plate I. The nerve fibres 

 enter the cord at the apex of the posterior horn ; some pass directly into the horn, traversing 

 the substance of Rolando, but the majority enter the horn from its median surface, passing 

 through what is known as the root zone of the posterior column on the way. Some of these 

 fibres are seen to end in the gray matter near the column of Clarke. Others may be traced 

 toward the anterior horn. The actual direction and destination of these posterior roots are 

 shown in the figure (see also Fig. 2, p. 18, and Fig. 3, p. 24). The anterior fissure of the 

 cord containing blood-vessels, and the posterior septum, are also shown in the plate. 



The white matter is made up of longitudinal fibres whose cut ends appear in the plate 

 as fine round white dots. In a normal cord thus stained there is no evident distinction 

 between the various columns of the white matter, though a posterior, lateral, and anterior 

 portion can easily be made out. The various columns as determined by pathological investigation 

 are as follows, and their situation is shown in Figs, i and 2. 



I. Anterior median column contains fibres from the motor cortex of the hemisphere which 

 have come through the pyramid of the medulla and have descended without decussating. These 

 fibres pass into the anterior gray matter and terminate in a fine brush-like expansion about 

 the cells of the anterior horn. They transmit impulses of voluntary motion. 



II. Antero-lateral column surrounding the anterior horn of the cord contains fibres passing 

 in both directions, which arise from cells lying in the anterior horn. These fibres pass from 

 the cells into the column, then bifurcate, turning both upward and downward, pass a long or 

 short distance through the column, giving off collateral branches in their course, then reenter 

 the anterior gray matter, and terminate, as do also the collaterals, in brush-like expansions 

 about the cells of the anterior horn. They transmit impulses of association which harmonize 

 the action of motor cells at various levels. This column is traversed by the anterior nerve 

 roots. 



