NEKVOUS SYSTEM. 



Direction of the Fibres after they have penetrated itie 

 Cord l)y ih^e Roots of the Spinal Nerves. In order to under- 

 stand fully the importance of this question, it is necessary to 

 bear in mind the following physiological facts : 



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. 



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

 disconnected from the rest of the cerebro-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 posi- 

 tive demonstration, we are prepared to study the anatomical 

 relations of the fibres and cells. In this, we cannot follow 

 minutely and critically discuss the elaborate investigations 

 of Stilling, Clarke, Kolliker, Yan der Kolk, Gerlach, Dean, 

 and others, without treating extensively of points which pos- 

 sess a purely anatomical and a more or less controversial in- 

 terest ; and we will content ourselves with the following very 

 recent description, quoted in full from Gerlach, which em- 

 bodies about all of our positive knowledge of the subject, 

 presented in the clearest manner possible. This extract, the 

 translation of which is almost literal, should be carefully 

 studied by those who desire to learn what is known at the 

 present day with regard to the physiological anatomy of the 

 cord. As a preparation for this study, it would be well to 

 closely examine Fig. 10, which gives a general view of the 

 different parts of the cord, shown in a transverse section : 



" With the present methods and means of investigation 

 at our command, we can scarcely give an exact, detailed de- 

 scription of the course of the fibres in the spinal cord, the 

 ground-work of the physiology of this organ. Investigations 



