MICROSCOPIC STRUCTURE. 13 



said to form the tissue ; some which are more conspicuous are known as the cells of 

 Deiters ; they appear stellate in section and are found in the larger interstices 

 between the nerve-fibres. Along the line of origin of the posterior roots the super- 

 ficial neuroglia dips inwards towards the horn of grey matter, and expands within it to 

 join the gelatinous substance of Rolando. This, as before mentioned, presents a 

 transparent jelly-like appearance in the fresh condition, but in sections of the 

 hardened cord it is finely reticular, containing numerous neuroglia-cells. Some of 

 the bundles of nerve-fibres of the posterior root traverse this substance, and it 

 contains many nerve-cells ; these are mostly of small size, but here and there one of 

 larger dimensions is met with. 



In the constitution of the rest of the cornua the neuroglia takes part to a far 

 less extent than in the substantia gelatinosa. It is true that it is prolonged both 

 from this and from the white substance into the grey matter, and pervades the 



Fig. 13. SECTION OP THE THO- 

 RACIC SPINAL CORD OF A CHICK 

 EMBRYO OP 9 DAYS INCCBATION, 

 STAINED BY GoLGl's METHOD. 



(Eamdn y Cajal. ) 



c, central canal ; v, ventral or 

 anterior ; d, dorsal or posterior 

 surface. The spongioblasts alone 

 are coloured and are seen to 

 extend from the central canal to 

 the periphery of the cord. Some 

 appear to be detached and in pro- . 

 cess of conversion into neuroglia- 

 cells. 



latter throughout in every 

 part. But it is in great 

 measure obscured by the 

 proper nervous elements, 

 which in the grey substance 

 comprise both cells and 

 fibres. In the first place are found multipolar nerve-cells, many of large size, 

 scattered singly or occurring in groups throughout the grey substance. In connec- 

 tion with these and especially accumulated around the cells and cell-groups, is an 

 interlacement of the finest nerve-fibrils, which is derived partly from the ramified 

 processes of the nerve-cells, and partly from the ramification of nerve-fibres or of 

 collateral fibres which enter the grey matter from the nerve-fibres of the white 

 columns. Occupying a considerable portion of the grey matter, are nerve-fibres, 

 mostly of the medullated kind ; these and the axis-cylinder processes of the nerve- 

 cells traverse the grey matter in different directions, coursing for the most part in 

 bundles which intercross with one another, and confer on the grey matter a spongy 

 appearance. Hence it is sometimes known as the substantia. spongiosa. 



Some of these bundles, which are fairly constant in position in many sections of the spinal 

 cord, have recently been described by Pal (see Bibliography). 



The structure of the neuroglia is described in the part of this work which deals 

 with General Anatomy (Vol. I., p. 322). It is developed from the spongioblasts of 

 His (see Embryology, Vol. I., p. 57), which at an early period of development 

 extend from the central canal in the middle of the grey matter to the periphery of 

 the cord (fig. 13). (The same holds good for other regions of the cerebro-spinal axis). 

 At a subsequent period their continuity from the central canal to the surface can no 

 longer be recognized, although it is certain that even in the adult the cells which line 



