632 FUNCTIONS OF THE CEREBRO -SPINAL NERVOUS SYSTEM. 



vaso-motor nerves. Considerable differences undoubtedly exist in the posi- 

 tion of the motor tracts in different parts of the Spinal Cord ; and M. Brown- 

 Sequard 1 concludes from his numerous experiments on the effects of section, 

 that whilst, in the dorsal region, all parts of the Spinal Cord except the 

 posterior columns are employed in the conveyance of the orders of the Will 

 to the muscles, in the upper part of the cervical region most of these con- 

 ductors are in the lateral columns, and in the gray substance between these 

 and the anterior columns, the latter here having little share in the transmis- 

 sion of such impulses. The same observer has satisfactorily shown that the 

 fibres which transmit motor impulses decussate almost exclusively at the lower part 

 of the Medulla Ol>longata. (See a r, Fig. 239. ) Hence if a section of one-half 

 of the Spinal Cord be made (as at 3, Fig. 239), loss of movement on the same 

 side occurs, in consequence of the division of the ascending motor fibres (ar) 



FIG. 23S. 



FIG. 239. 



FIG. 238. A, Posterior Column. B, Posterior horn of gray matter, c, Anterior horn of gray matter- 

 D, Antero-lateral column. E, Loop-fiiires of the posterior column proper. F, A posterior nerve-root. 

 G, Ascending fasciculus of this root, n, Direct fasciculus. I, Descending fasciculus. J, Reflex motor 

 root. K, Chain of sensory cells, j,. Chain of motor cells, m, Encephalic fibres of the anterior columns. 

 N, Anterior nerve-roots. D, Loop fibres of the anterior roots. 



FIG. 239. Diagram showing the course of the Motor and Sensory Fibres in the Spinal Cord and 

 Medulla Oblongata. 



from the anterior roots ; whilst if the section be made at the level of the de- 

 cussation of the anterior pyramids (as at 2), paralysis of the muscles of both 

 sides is produced ; lastly, if a section be made a little higher (as at 1), paralysis 

 of the muscles of the opposite side results. Numerous fibres belonging to the 

 anterior roots undoubtedly decussate throughout the greater part of the Spinal 

 Cord ; but these are probably destined, as suggested by Brown-Sequard, to 

 be channels for the conveyance of reflex actions. Schiff proposes the term 

 "kinesodic 2 substance" for the material by which motor impulses are con- 

 veyed along the Spinal Cord, on the ground that when directly stimulated 

 the movements performed are few and imperfect ; and he thinks that as with 

 the "se.sthesodic substance," so with the "kinesodic substance," the smallest 

 portion is capable of transmitting motor impulses in any direction. From 

 the results of the foregoing experiments, which are fairly in accordance with 

 the microscopic analysis of the cord given by Lockhart Clarke ( 481) and 

 others,' it, may be concluded, 1. That sensory impressions are conducted to 

 the spinal cord by the posterior roots of the spinal nerves; that the fibres of 

 these roots diverge on entering the cord, some passing directly across to the 



1 Op. cit., p. 46. 2 From nh't/a/e, motion, and 666$, a putl). 



:i For ronlinnalory evidence, see M. Brown-Sequard 's treatise; Schiff, Op. cit. ; 



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H. Sunders, Ilenlc and Mi-Usner'a Bericht. 



