THE SPJXAL CORD 737 



INTERNAL STRUCTURE OF THE SPINAL CORD 



In transverse section, each lateral half of the cord is seen to be composed of 

 !)oth grey and white matter, the latter being disposed on the surface. The grey 

 matter is in the form of a crescent, which has been not inaptly compared (by Testut) 

 to a large comma ( * ). The head of the comma looks forwards and constitutes the 

 anterior horn of grey matter; the tail forms the posterior horn, and the convexity 

 looks inwards and is united to the grey crescent of the opposite side by the grey 

 commissure. The two crescents, with the commissure, form a figure resembling a 

 capital H. Within the grey commissure is the central canal of the cord, and in 

 front of the grey commissure, occup3ang the floor of the anterior longitudinal 

 fissure, is the anterior white commissure. Medullated fibres cross the middle line 

 both in the white and in the grey commissure. The term commissure is somewhat 

 misleading, as the majority of the nerve-fibres which pass from side to side are not 

 commissural l:)ut decussating fiV>res. 



The grey matter of the cord consists of two varieties: (a) Substantia gelatinosa, 

 and (6) substantia spongiosa. The former (a) covers the head of the posterior 

 horn like a cap fsubstantia gelatinosa Rolandi ), and is also foimd around the 

 central canal (substantia gelatinosa centralis ). The latter is continued into the 

 ependyma of the cerebral ventricles, (b) The substantia spongiosa is much more 

 extensive than the substantia gelatinosa, and contains large nerve-cells. Tliese 

 cells are arranged in definite groups, forming columns in the grey matter. 



The cell columns in the anterior cornua are arranged as follows: 



i Dorso-niesial. 

 1 

 Mesial (fig. 440 A;. I 



These colunms are the most 

 constant in all situations, 

 and are Ijelieved to supply 



[ Ventro-mesial. [ the spinal muscles. 



Best marked o})j)osite the 



r Dorso-lateral. \ limb nerves to which they 



T 1 ,^ . ./v A ! ^ ^ive origin. 



Lateral (fig. 440 A), j ^ In cervical region, gives 



I ,. , , i-ateral. -j^ origin to spinal accessory. 



\entro-lateral. -, ^^.^^^ ^ j^^ ^^^^ ^,^^.^^^ ^-^ 



I- t. origin to phrenic nerve. 



The cells of the posterior cornu. — The cells of the ])osterior cornu are less 

 regular tlian those of the anterior cornu in arrangement, but several groups are 

 describi^l. They are (1) peripheral cells, some of which possess long, curved j)ro- 

 cesses, and hence are called coinet cells; (2) central cells; (3) basal cells; (4) the 

 cells of the substantia gelatinosa; and (5) solitary cells, which are scattered irreg- 

 ularly and which vary in size. The protoplasmic or dendritic processes of the cells 

 of the })Osterior cornu permeate the gray matter of the cornu; their axis-cylinder 

 processes or axons run in various directions, and their terminations are for the most 

 ])art unknown; some of them, however, pass to the anterior cornu and to the 

 anterior connnissure, and these are believed to issue from the cord as the snudl 

 fibres of till' anterior nerve-roots. 



Clarke's column of cells (fig. 440 A). — This column of cells lies at the Itase of 

 the posterior cornu internally. It consists of large ovoid cells whose long axes are 

 parallel with the axis of the cord. The column is limited to the dorsal region, 

 but cells of similar nature, occupying a similar position, are found in the lumbar 

 region of the cord opposite the second and third sacral nerves, where they foim 

 Stilling' s nucleus. Others are recognisable in the cervical region, and they are 

 probably represented in the medulla by the cells of the nucleus gracilis and the 

 nucleus cuneatus. Many of the axons of the cells of this column pass upwards to 

 tlie cerebellum in the dorso-lateral ascending cerebellar tract, and some are probal'ly 

 distriV)uted. as anabolic or inhibitory nerves, to the blood-vessels, glands, and to 

 the walls of tli<' aliineiitarv canal. 



The intermedio-lateral tract. — Tlie intermedio-lateral tract or column of 

 47 



