INTERNAL STRUCTURE OF THE CORD. 



507 



matter, which runs along the surface of the lateral column, and is separated from it 

 by a streak of greyish substance. According to the same authority, this narrow tract 

 enlarges above, and may be traced upwards along the side ot the medulla oblongata 

 into the cerebellum. (Op. cit. p. 285.) 



Fig. 343. 



Fig. 343. DIFFERENT 

 VIEWS OF A PORTION OF 

 THE SPINAL CORD FROM 

 THE CERVICAL REGION 

 WITH THE ROOTS OP 

 THE NERVES. Slightly 

 enlarged. 



In A, the anterior sur- 

 face of the specimen is 

 shown, the anterior nerve - 

 root of the right side 

 being divided ; in E, a 

 view of the right side is 

 given ; in C, the upper 

 surface is shown ; in D, 

 the nerve-roots and gan- 

 glion are shown from 

 below. 1, the anterior 

 median fissure ; 2, pos- 

 terior median fissure ; 3, 

 anterior lateral depres- 

 sion, over which the ante- 

 rior nerve-roots are seen 

 to spread ; 4, posterior 

 lateral groove, into which 

 the posterior roots are 

 seen to sink ; 5, anterior 

 roots passing the ganglion ; 

 5', in A, the anterior root 



divided; 6, the posterior roots, the fibres of which pass into the ganglion, 6' ; 7, the 

 united or compound nerve ; 7', the posterior primary branch seen in A and D, to be 

 derived in part from the anterior and in part from the posterior root. 



Internal structure of the spinal cord. The spinal cord consists of white 

 aiid grey nervous substance. The white matter, forming by far the larger 

 portion of the cord, is situated externally, whilst the grey matter is dis- 

 posed in the interior. 



The grey matter, as seen in a transverse section of any part of the cord, 

 presents two crescent-shaped masses, placed one in each lateral half, with their 

 convexities towards one another, and joined across the middle by a transverse 

 portion, the grey or posterior commissure of the cord. Each of these grey 

 crescents has an anterior and a posterior cornu or horn. The posterior, 

 generally longer and narrower, approaches the posterior lateral fissure : the 

 anterior, shorter and thicker, extends towards the place of attachment of the 

 anterior roots of the nerves. In front of it a layer of white substance 

 separates it from the bottom of the anterior median fissure, this is named 

 the anterior white commissure. 



Another white layer, very thin and indistinct, was formerly described as lying 

 behind the grey commissure; but in the present state of our knowledge it seems 

 sufficient to describe one white commissure, and one grey commissure behind it. 



At the back part or tip of the posterior horn, which is somewhat en- 

 larged, the grey matter has a peculiar semitransparent aspect, whence it 

 was named by Rolando substantia cinerea gelatinosa : the remaining and 



L L 2 



