342 THE SPINAL CORD, BY J. GERLACH. 



tudinal sections (fig. 229, g). A portion of the fibres belong- 

 ing to the posterior roots namely, the lateral ones preserve 

 a purely horizontal course in the white substance, and run 

 directly into the substantia gelatinosa of the posterior cornua ; 

 the middle set of the posterior root fibres, on the other hand 

 (fig. 221, /), curves in that part of the posterior columns which 

 bounds the substantia gelatinosa, and ascending in a vertical 

 direction, and perhaps also descending for a variable distance 

 in the posterior columns, ultimately curves again to enter 

 the grey substance of the posterior cornua lying in front of 

 the substantia gelatinosa (fig. 221, g). 



The anterior roots of the nerves belong to the oblique system 

 of fibres traversing the white substance of the spinal cord. 

 In perfectly level transverse sections, consequently, they can 

 only be seen in a partial and fragmentary manner (fig. 217, d), 

 whilst in sagittal longitudinal sections the obliquity of their 

 course is very apparent (fig. 229, 6). Oblique fibres are 

 also found in the highest part of the cervical region of the 

 cord, and still more distinctly in the medulla oblongata. These 

 fibres belong to the inner portion of the lateral columns, and run 

 medially and forwards ; they are, in truth, the commencement 

 of the decussation of the pyramids, which however becomes 

 most marked and complete in the medulla oblongata. 



THE GREY SUBSTANCE OF THE SPINAL CORD. 



As in the white, so in the grey substance of the spinal cord, 

 the neuroglia or tissue belonging to the class of connecting 

 substances is abundantly present. It forms the support of the 

 nervous elements of the grey matter, and is continuous with 

 the similar material of the white substance. The septum 

 posterius, however, as well as the other septula of the white 

 columns, lose on entering the grey substance their fibrillated 

 appearance, and assume the histological characters of that 

 tissue which we now know to be the connecting substance 

 occupying the interspaces of the several nerve fibres of the 

 white substance. This tissue presents some peculiarities in 

 the immediate neighbourhood of the central canal, and in that 

 part also of the posterior cornua which has received the name 

 of substantia gelatinosa, and which will be subsequently de- 



