STRUCTURE OF THE SPINAL CORD. 001 



on the other hand, are largest at the lowest part of the dorsal region. The 

 delicately granular nucleated substance which intervenes between the cylin- 

 der-axes of the gray substance of the spinal cord, and forms the greater 

 part of it, was termed "neuroglia" by Virchow, " reticulum" by Kolliker, 

 "granular basement-substance" by Henle, "spongy substance" by Schultze, 

 and is believed by Henle, 1 Robin, 2 and others to be quite distinct from con- 

 nective tissue, not only in function, but in microscopical characters, and in its 

 chemical reactions. 'Gerlach 3 and Frey, 4 however, still describe it as a spe- 

 cial form of connective tissue. It is chiefly found at the periphery of the 

 nervous centres, where it forms a cortical envelope around the central canal 

 of the cord (forming the noyau periependymaire of the French writers) on the 

 two surfaces which bound the posterior median fissure, and lastly, around 

 the posterior cornua, where it forms the gelatinous' substance of Rolando. 

 It is described by Gerlach 5 and Lockhart Clarke as a material of finely 

 granular aspect, like the matrix of hyaline cartilage, with little clumps of 

 cytoid particles scattered through it, which seem to be in connection with the 

 cells lining the central canal, and with the pia mater. Pervading every 

 part of the ueuroglia of the gray substance of the cord, 'except that lying 

 in immediate proximity to the central canal, is a close plexus of extremely 

 fine fibres, chiefly derived from the processes of the nerve-cells just described. 

 The bloodvessels of the central parts of the nervous system are stated by 

 His 6 to be surrounded by a loose sheath, between which and the proper 

 external coat lymph-corpuscles are perceptible. These spaces he considers 

 to represent the lymphatic system of these parts, which are otherwise desti- 

 tute of this system of vessels. 



482. The connection of the Nerve-roots of the Spinal Nerves with the 

 several components of the Cord, and the course of the fibres after entering 

 it, may be made out partly by means of sections, and partly by following 

 the course of individual fibres by ordinary microscopical dissection. 7 The 

 following is an outline of the information which may thus be gained from a 

 comparison of transverse and longitudinal sections (Fig. 207 et seq.). The 

 bundles that form the Posterior roots (Fig. 207, c, c ; Fig. 210, P, P, P ; Fig. 

 211, g) consist of three kinds, which differ from each other partly in direc- 

 tion, and partly in the size of their component filaments. The first kind, 

 Fig. 210, a, a, a (which are more numerous in the upper part of the Cord), 

 enter the posterior columns horizontally ; and then, taking a longitudinal 

 direction down the Cord, send fibres into the anterior gray substance (G), of 

 which some bend upwards, and others downwards ; part apparently be- 

 coming continuous with fibres of the anterior roots; whilst another part lose 

 themselves among the fibres of the anterior columns, in which they may 

 either proceed continuously to the head, or may pass along for a limited 

 distance only, to emerge in the nerve-roots of some other segment. The 

 second kind of bundles, b, b, b, also traverse the posterior columns horizon- 

 tally and obliquely inwards ; their further course may be best traced in a 

 transverse section (Fig. 207). These fasciculi, which are composed of re- 



1 Centralblatt, 1869, p. 117. 



2 Anatomic et Physiologic Ccllulaires, 1873, p. 117. 



3 Strieker's Hum. "and Coinp. Histol., Syd. Sue. Trans., vol. ii, p. 335. 



4 Histolocry, Barker's Transl., p. 575. 



5 Centralblatt, 1867, N<>s. '24 and 35. 



6 Siebold and Kolliker, Z.-itschrift, Bel. xv, 1865, p. 127. 



7 Mr. J. L. Clarke has succeeded, by the adoption of a peculiar method of prep- 

 aration (for which see Phil. Trans., 18158, p. 321). in making sections of considerable 

 thickness sufficiently transparent to allow the course of the tibres, and the contour of 

 the nerve-cells and their prolongations, to bo distinctly made out. 



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