THE SPINAL CORD. 



WHEN examined in transverse sections, the spinal cord of a reptile or 

 batrachian, like that of the higher vertebrates, is found to be composed 

 of two substances, the white and the gray, and, in most cases, the natu- 

 ral division into six columns is to be observed in the white substance. 



The superior (posterior) median fissure does not exist as such, its 

 position being marked, much as in man, by a membrane which extends 

 vertically downwards from the pia mater, dividing into halves the por- 

 tion of the white substance included between the superior roots of the 

 spinal nerves. 



Gerlach states that in man : "Both portions of the pia mater extend 

 to the bottom of the anterior fissure, that is to say, as far inward as the 

 anterior white commissure, while only the adherent layer of the pia ma- 

 ter sinks directly down into the posterior fissure to the gray commissure. 

 This posterior septum unites the posterior columns so closely that a 

 posterior fissure can not well be said to exist in the strict meaning of the 

 word." 



Figures 240 & 241, in his contribution to Strieker's manual of his- 

 tology, show, after removal of the pia, a well marked posterior fissure. 

 As this never appears in reptiles, it is fair to conclude that the union of 

 these columns is closer than in man. Plates I. II. & III. illustrate the 

 six divisions into columns above referred to. 



In saurians, between the inferior white and gray commissures, two 

 longitudinal bundles of white nerve fibres extend from the posterior lum- 

 bar region well into the medulla oblongata, where they form on each 



