PHYSIOLOGICAL ANATOMY OF THE SPINAL CORD. 



671 



tions. In addition, fine, branching poles are described under the name of protoplasmic 

 prolongations. 



The direction of the fibres in the cord is one of the most difficult and complicated 

 problems in physiological anatomy ; and, especially as regards the posterior roots of the 

 nerves, it is one which cannot as yet be elucidated by purely anatomical investigations, 

 but requires the aid of experimental and pathological observations. In order to under- 

 stand fully the importance of this question, it is necessary to bear in mind the following 

 physiological facts, which it is desirable, if possible, to explain by the anatomical rela- 

 tions and connections of the fibres and cells : 



1. The cord serves as a conductor of impressions to the brain, conveyed to it through 

 the posterior roots, and of stimulus generated by the brain and passing from the cord 

 by the anterior roots of the spinal nerves. This action is crossed, the decussation taking 

 place mainly at the medulla oblongata, for the anterior portions, and throughout the 

 whole extent of the cord, for the posterior portions. 



FIG. 223. Transverse section of the spinal cord of a child *?> months ol<L (it the middle of the I umlar enlarge- 

 ment, t/- ,'(>'/ iritli, potasrio-chlorid* of gold and nitrate of uranium; magnified 20 diameters. Bu 

 means of these reagent*, the direction of the fibres in the gray substance is rendered unusually distinct. 

 (Gerlach.) 



a, anterior columns; &, posterior columns ; c, lateral columns ; d, anterior roots ; e, posterior roots : /. anterior white 

 commissure, in communication with the fasciculi of the anterior cornua and the anterior columns : (/. centra] 

 canal with its epithelium; h, surrounding connective substance of the central canal; /. transverse fasciculi ot 

 the gray commissure in front of the central canal; k, transverse fasciculi of the gray commissure behind toe 

 central canal; /, transverse section of the two central veins ; m. anterior cornua : >t, great, lateral cellular layer 

 of the anterior cornua; <>. lesser, anterior cellular layer; />, smallest, median cellular layer; q, posterior cornua; 

 r, ascending fasciculi in the posterior cornua; s, substantia gelutinosa. 



2. Independently of its action as a conductor, the cord, disconnected from the rest of 

 the eeivbro-spinal axis, acts as a nerve-centre, by virtue of its gray matter and the fibres 

 connected with the cellular elements of this substance. 



Bearing in mind these points, which are matters of positive demonstration, we are 

 prepared to study the anatomical relations of the fibres and cells. In this, we shall con- 



