508 



THE SPINAL CORD. 



greater part of the grey matter, which resembles that most generally preva- 

 lent, was named by Rolando the substantia spongiosa. 



The grey cornua vary in form in different parts of the cord : thus they 

 are long and slender in the cervical portion, still more slender in the dor- 

 sal, and shorter and wider in the lumbar region. The grey matter appears 

 in a series of sections to be, relatively to the white, more abundant in the 

 lumbar region of the cord, less so in the cervical region, and least so in the 

 dorsal. The actual amount, however, of white matter is greatest in the 

 neck. Towards the lower end of the cord, the double crescentic form 

 gradually disappears, and the grey matter is collected into a central mass, 

 which is indented at the sides. At its extreme point, according to Remak 

 and Valentin, the cord consists of grey matter only. 



Fig. 344. 



Fig. 



344. SECTIONS OF THE SPINAL 

 CORD IN DIFFERENT PARTS. 



These views are taken partly from 

 Stilling's plates and partly from nature. 



A, is a section through the middle of the 

 cervical enlargement, at the root of the 

 sixth cervical nerve; B, through the mid- 

 dle of the dorsal cylindrical portion ; C, 

 through the middle of the lumbar enlarge- 

 ment ; D, in the conical diminishing part 

 of the cord ; E, farther down at the 

 origin of the fifth sacral nerve ; F, at 

 that of the coccygeal nerve ; Gf, is a sec- 

 tion of the part where the conus medul- 

 laris begins to pass into the filum termi- 

 nale ; and H, at the lower part of this 

 or in the commencement of the filum 

 terminale. 



A, B, and C, are fully twice the natural 

 size ; D, E, and F, about three times ; 

 and Gr and H, about six times. In A, 

 and C, a, marks the .interior root- fibres 

 of the nerves ; and p, the posterior root- 

 fibres as they enter the spinal cord. In 

 D, E, and F, the great diminution of the 

 white substance in proportion to the grey 

 is seen ; in G-, the peculiar form of the 

 central canal and medullary substance 

 covering it ; and in H, the open con- 

 dition of the central canal posteriorly. 



In all the figures the position is the 

 same, viz., the anterior part placed down- 

 wards. 



Central canal. Extending through the whole length of the spinal cord, 

 in the substance of the grey commissure, there is a minute central canal 

 which in prepared transverse sections of the cord is barely visible, as a 

 speck, with the naked eye. Superiorly, it is continued into and opens out 

 at the calamus scriptorius of the fourth ventricle ; and inferiorly, it is 

 prolonged into the filum terminale. It is lined with a layer of cylindrical 

 ciliated cells or epithelium. This canal, though minute, is an object of 

 considerable interest as a typical part of the structure of the cord, it being 

 the permanent remains of the cavity of the cylinder formed by the spinal 

 cord at the earliest period of its development. It is more distinctly seen 



