THE SPINAL CORD. 



671 



Fig. 320. 



in the inferior, and one in the superior grey cornu. The columns cor- 

 respond to what Stilling has named the nuclei of the nerves. A foui'th 

 mass ot cells, the superior vesicular column 

 of Clarke, or dorsal nucleus of Stilling, is 

 observed at the point where the grey com- 

 missure joins the cornua. The nerve-tubes 

 (or tubules) aflfect longitudinal, transversal, 

 oblique, and vertical directions. 



They bring the cells of one lateral 

 moiety of the meduUa into communication 

 with : 1, The tubes of the white substance ; 

 2, Each other ; 3, The cells of the opposite 

 moiety, by passing into the commissures ; 

 4, The tubes of the white substance of the op- 

 posite moiety, by following the same course. 



The neuroglia and nerve-tubes consti- 

 tute the white substance, which is decom- 

 posed, as we know, into three cords. All 

 the tubes of this substance do not ascend 

 to the brain, as was believed for a long time ; 

 the opinion that the tubes of the spinal 

 nerves formed the medulla and extended to 

 the brain, has been abandoned since Volk- 

 mann measured, comparatively, the section 

 of all these nerves and that of the nervous 

 spinal-axis. 



(Volkmann has established the fact, that 

 the size of the medulla corresponds with the 

 number of nerve-tubes given off at any point. 

 He gives the weight of four segments, each 

 2^ inches in length, from the spinal cord 

 of the Horse, and the relative extent of the 

 grey matter in square lines; these are as 

 follows 



Area Area 



Grains, of Grey of White 



Matter. Matter. 

 Frombelow2nd Spinal Nerve, 219 13 109 



„ „ 8tll „ „ 293 28 142 



„ 19th „ „ 163 11 89 



„ „ 30th „ „ 281 25 121) 



In the white substance the tubes are lon- 

 gitudinal, oblique, or transversal ; the latter 

 arise from the cells of the grey substance, 

 and represent the roots of the nerves 

 emerging either by the superior or inferior 

 collateral fissure. 



The tubes of the anterior cords pass to 



LONGITUDINAL SECTION THROUGH 

 CERVICAL ENLARGEMENT OF SPINAL 

 CORD OF OAT. 



AC, Inferior white columns ; AC', Por- 

 tion showing the arrangement of 

 the longitudinal fibres \ PC, Pos- 

 terior white columns ; G, Grey- 

 substance between them(theTesicles 

 being omitted to avoid obscuring 

 the course of the fibres) ; A, Anterior roots of the nerves , P, Posterior roots, consisting 

 of three kinds : the first, a, crossing the posterior columns horizontally, and then pass- 

 ing obliquely downwards, across the grey substance, into the anterior columns ; the 

 second, b, traversing the posterior columns horizontally, and then losing themselves 

 in the grey substance ; the third, c, for the most part becoming continuous with the 

 longitudinal fibres of the posterior column ; all, or nearly all, ultimately entering the 

 grey substance. 



