446 THE SPINAL CORD. 



The exact termination of the nerve fibres in the gray substance of the 

 cord is a matter of much importance, but which is not yet fully eluci- 

 dated. The strong probability is 'that some of the fibres of the anterior 

 nerve roots are directly connected with radiating nerve cells in this 

 locality by means of the long axis-cylinder processes of these cells ; but 

 the most accomplished and careful microscopists have found it impos- 

 sible to actually see this connection. Its probability rests upon the 

 facts that, first, the long processes of the nerve cells in the anterior 

 horns closely resemble, as their name indicates, the axis-cylinder of the 

 nerve fibres ; and, secondly, these processes are often seen, in horizontal 

 or antero-posterior vertical sections, to pass forward toward the origin 

 of the anterior root fibres, and emerge, in company with them, from the 

 gray into the white substance of the cord. 1 Beside these fibres, how- 

 ever, others, forming a part of the anterior nerve roots, pass distinctly, 

 according to Kolliker, from the gray substance of the anterior horn into 

 the white commissure, and thence, crossing t the median line, into the 

 anterior column of white substance on the opposite side ; while others, 

 radiating backward and outward, may be seen to emerge from the ex- 

 ternal border of the gray substance, and to join the longitudinal fibres 

 of the lateral column on the same side. 



Thus it is certain that the immediate connection of all the fibres of 

 the anterior nerve roots is with the gray substance of the anterior 

 horn ; but some of them pass subsequently to the anterior column of 

 the opposite side of the cord, others to the lateral column of the same 

 side. 



The posterior roots are distinguished from the anterior, first, by the 

 generally smaller size of their nerve fibres ; secondly, by the presence 

 of the ganglia, known as the " spinal ganglia," or the ganglia of the 

 spinal nerve roots, The gray substance of these ganglia contains nerve 

 cells which are distinguished from those of the spinal cord by not pos- 

 sessing ramified prolongations. They present, however, often one, 

 sometimes two or more, pale, unbranched axis-cylinder processes, which 

 subsequently become continuous with medullated nerve fibres, running 

 outward with the other nerve fibres toward the periphery. These ganglia 

 therefore give origin to additional nerve fibres, which afterward form 

 part of the trunk of the spinal nerve. The fibres of the posterior nerve 

 roots, on the contrary, coming from the spinal cord, according to Kolli- 

 ker, only traverse the gray matter of the ganglion, without making any 

 anatomical connection with its substance. 



The fibres of the posterior roots, on entering the spinal cord, between 

 its posterior and lateral columns, pass into the posterior horns of gray 

 matter ; after which some of them change their direction and become 

 longitudinal, still remaining in the gray substance, others become trans- 



1 Kolliker, Elements d'Histologrie Humaine. Paris, 1868, p. 343. Gerlach, in 

 Strieker's Manual of Histology, Buck's edition. New York, 1872, pp. 636, 637. 



