562 PHYSIOLOGY OF THE NERVE CELL AND THE SPINAL CORD 



It must be observed, however, in this connection, that our knowledge con- 

 cerning the finest structure of the nervous system, especially in the vertebrates, 

 is still too meager to admit of any one satisfactory or conclusive view. 



2. THE STRUCTURE OF THE SPINAL CORD 1 



A cross section of the spinal cord (Fig. 254) shows the central gray matter 

 with its contained nerve cells, and surrounding it the white matter made up 

 of nerve fibers. The anterior longitudinal or median fissure (a) and the pos- 



FIG. 254. Semidiagrammatic section of the spinal cord, after Erb. a, anterior fissure; b, pos- 

 terior septum; c, anterior column; d, lateral column; e, posterior column; /, funiculus gracilis; 

 g, funiculus cuneatus; h, anterior root; i, posterior root; k, central canal; I, sulcus inter- 

 medius posterior; ra, cells of the anterior horn; n, cells of the posterior horn; o, lateral horn; 

 p, processus reticularis; q, anterior commissure; r, posterior commissure; s, Clark's column. 



terior median septum (&) divide the cord into two symmetrical halves, con- 

 nected by two commissures (q, r), the anterior white and the posterior gray 

 commissures. 



The gray matter, pierced in the middle by the central canal (&), has in 

 general the appearance of the capital letter H, but varies somewhat in form 

 at different levels. The roots of the nerves enter each half of the cord in sepa- 

 rate bundles, the posterior and the anterior spinal nerve roots. These divide 

 the white matter into three main portions: (1) the anterior column lying between 

 the anterior longitudinal fissure and the anterior nerve root; (2) the lateral 

 column lying between the anterior and posterior nerve roots; (3) the posterior 

 column lying between the posterior nerve root and the posterior median septum. 



1 After Edinger's " Vorlesungen iiber den Bail der Nervosen Zentralorgane," seventh 

 edition, Leipzic, F. W. C. Vogel, 1904. Since the more recent views, as set forth in 

 the paragraphs above, on the structure of the nervous system are still immature, and 

 fall short of a comprehensive exposition of the structure of the spinal cord, in the account 

 here and in that which follows we shall make use of the anatomical facts thus far estab- 

 lished without further reference to the relation and connection which may exist between 

 the individual cells and fibers. 



