654 



NERVOUS SVSTEM. (NERVOUS CEDTIIES. THE SPINAL CORD.) 



and the grey matter, and remarkable varieties 

 as regards the shape of the lateral portions of 

 the latter. The relative proportion of the grey 

 matter to the white appears to be much greater 

 in the lumbar than in the cervical or dorsal 

 regions. In the upper part of the cord the 

 crescentic portions are narrow, and the white 

 matter is abundant. The posterior horn ap- 

 pears as a thin lamella extending back to the 

 surface, while the anterior is a small, roundish, 

 slightly stellate mass, remote from the surface 

 of the anterior columns. In the dorsal region 

 the grey matter is at its minimum of develope- 

 ment : here it appears much contracted and 

 diminished iu size, although presenting the 

 same general form as that in the region of the 

 neck. In the lumbar region both horns acquire 

 a manifest increase of thickness, the posterior 

 still extending back quite to the surface, and 

 the anterior, more stellate than in the higher 

 parts of the cord, separated from the corre- 

 sponding surface of the cord by a much 

 smaller quantity of white substance. At a 

 still lower part of the cord, where the lumbar 

 swelling begins to diminish in size, the pos- 

 terior horn is short and thick, and some- 

 times seems not to reach quite back to the 

 surface of the cord, an appearance, however, 

 which might be produced by some accidental 

 obliquity of the section; and its posterior 

 extremity has somewhat of the form of a 

 hook, its hindermost portion being directed 

 a little forwards and inwards, forming a very 

 sharp angle with the rest of the grey sub- 

 stance which constitutes the horn. At the 

 lowest part of the cord the crescentic form of 

 the lateral portions of grey matter ceases, and 

 the transverse section of if presents the form of 

 a solid cylinder slightly notched on each side, 

 and surrounded completely by the white sub- 

 stance. (Fig. 377.) 



There are also differences deserving of notice 

 as regards the white substance in the different 

 regions of the cord. The largest quantity of 

 white substance is found in the cervical en- 

 largement, as may be shown on a transverse 

 section. Both the antero-lateral and the pos- 

 terior columns are large, but by far the greatest 

 proportion of the mass of white substance must 

 be assigned to the antero-lateral columns. It 

 is also important to remark that the quantity of 

 white substance which is placed between the 

 posterior horns in a great part of the cervical 

 region is augmented by the existence of two 

 small columns of white matter, which will be 

 more particularly described when we come 

 to speak of the medulla oblongata. These 

 columns extend from the inferior extremity of 

 the fourth ventricle, very nearly as far down 

 as the termination of the cervical enlarge- 

 ment, where they gradually taper to a fine 

 point and disappear, allowing the posterior 

 columns of the cord to come into apposition 

 along the posterior fissure. These small co- 

 lumns, the posterior pyramids of some authors, 

 do not appear to be completely isolated from 

 the proper posterior columns of the cord. There 

 is generally a very clear line of demarcation 

 between them, visible on the posterior surface, 



1 



r A 



by a distinct depression or 

 fissure which passes in the 

 length of the cord ; but 

 this fissure does not extend 

 much deeper than the sur- 

 face, nor does any distinct 

 process of pia mater sink 

 into it. Nevertheless, in 

 the spinal cord, which has 

 been hardened in alcohol 

 or by any other chemical 

 reagent, these columns will 

 readily separate by tearing 

 in the longitudinal direc- 

 tion, both from each other 

 and from the posterior 

 columns between which 

 they are placed. They 

 occupy rather less than 

 one-half of the interval be- 

 tween the posterior roots of 

 the nerves, excepting at 

 their lowest part, where, 

 from their tapering form, 

 they obviously take up 

 much less space. 



In the dorsal region 

 both white and grey mat- 

 ter are small in quantity ; 

 the posterior columns, how- 

 ever, do not appear to ex- 

 perience a diminution in 

 size at all commensurate 

 with the general shrinking 

 of the organ in this region, 

 nor with the reduced size 

 of the antero-lateral co- 

 lumns. 



In the lumbar region 

 the antero-lateral columns 

 Transverse sections of are small ; the grey matter 

 the spinal cord. i s i ar g e i n quantity, and 

 (After Arnold.) thfi posterior co l umns ap _ 



1. cervical region at . , . . t 

 the upper part of P ear to '' etain tllelr Slz e = 

 the swelling. they are, indeed, propor- 



2, the same at the tionally to the other parts 

 largest part of the o f the cord, larger in this 

 swelling. fa &n m ^ cerv j ca l region, 



o, dorsal region. ,,. 



4, lumbar region. and the lumbar Swelling 



5, pointed extremity, appears to depend much 

 A, anterior surface, more upon the large size 

 P, posterior surface. o f the grey matter and of 

 the posterior columns than upon the bulk of the 

 antero-lateral ones. At the lowest point of 

 the cord the white matter has gradually disap- 

 peared, and in the commencement of the ter- 

 minal filiform process grey matter only is pre- 

 sent, according to Remak and Valentin. 



These facts lead to some interesting physio- 

 logical conclusions bearing upon the function 

 of the cord as well as of its columns. It i s 

 in the upper extremities that voluntary power 

 and sensibility are in their most highly deve- 

 loped state, and accordingly the size of that 

 portion of the cord from which the nerves of 

 these parts emanate is greater than any other 

 portion of the cord. Were the sensibility de- 

 pendent on the grey matter or upon the pos- 

 terior columns, as has been conjectured, it 



