CH. XLV.] 



STRUCTURE OF THE SPINAL CORD 



649 



tinctly above) by two longitudinal furrows, which divide it into three 

 portions, columns, or tracts, an anterior, lateral, and posterior. From 

 the groove between the anterior and lateral columns spring the 

 anterior roots of the spinal nerves (fig. 399, B and c, 5) ; and just 

 in front of the groove between the lateral and posterior column the 



FIG. 399. Different views of a portion of the spinal cord from the cervical region, with the roots of the 

 nerves (slightly enlarged). In A, the anterior surface of the specimen is shown ; the anterior nerve- 

 root of its right side is divided ; in B, a view of the right side is given ; in c, the upper surface is 

 shown ; in r>, the nerve-roots and ganglion are shown from below. 1, the anterior median fissure ; 

 2, posterior median fissure ; 3, anterior lateral depression, from which the anterior nerve-roots are 

 seen to issue ; 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. 

 (Allen Thomson.) 



posterior roots enter (B, 6) : a pair of roots on each side corresponds 

 to each vertebra. 



White matter. The white matter of the cord is made up of 

 medullated nerve-fibres, of different sizes, running mainly in a 

 longitudinal direction, and of a supporting material of two kinds, 

 viz. : (#) ordinary fibrous connective tissue with elastic fibres, which 

 is connected with septa from the pia mater which pass into the cord 

 to carry the blood-vessels, (b) Neuroglia; the processes of the 

 neuroglia-cells are arranged so as to support the nerve-fibres, which 

 are without the usual neurilemmal nerve-sheaths. 



The general rule respecting the size of different parts of the cord 

 is, that each part is in direct proportion to the size and number of 

 nerve-roots given off from it. Thus the cord is very large in the 



