TEK SPINAL CORD. 



761 



branous bodies of which, irregularly stellate, send 

 numerous prolongations between the nerve-tubes 

 and cells. 



(In the substantia gelatinosa on the superior 

 surface of the cord is a network of fine fibrils, 

 epithelial in its nature, and consisting of cuticiilar 

 matter ; this is known as the granular matter, 

 or spongy horn-substance.) 



The fibres and cells form, with the neuroglia, 

 the whole of the grey substance. 



The cells have a more or less large number 

 of protoplasmic prolongations which ramify and 

 anastomose, or have a process — the prolongation 

 of Deiters — which puts them in communication 

 with a nerve-tube. They are more or less 

 voluminous. 



The fibres of the grey substance are all very 

 fine, and some have a sheath of myeline ; the 

 others are reduced to an axile filament. 



In the Horse, the cells are not universally 

 distributed throughout this substance, but are 

 collected in small masses Avhich form longitudinal 

 columns. The largest are grouped in three small 

 masses around the inferior cornu — one external, 

 another internal, and the third at the extremity ; 

 the latter is the most considerable. They are 

 in relation with the motor roots of the nerves. 



Some are spread in the middle part of the 

 grey substance, and principally opposite the point 

 where the grey commissure joins the cornua. 

 There they form Lochhart Clarke''s column. 



A small number are placed on the margin 

 of the superior grey cornu, and these, as well as 

 the cells of Clarke's column, receive radicular 

 filaments from the spinal sensory nerves. 



Finally, some form an external column 

 {column of Burdach) at the junction of the two 

 cornua, whence emerges, above, the small nerve 

 of Wrisberg. They are probably connected with 

 the vaso-motor phenomena. 



The nerve-tubes (or tubules) affect longi- 

 tudinal, transversal, oblique, and vertical direc- 

 tions. They bring the cells of one lateral moiety 

 of the medulla into communication with : 1. 

 The tubes of the white substance which pass 

 towards the brain. 2. Each other. 3. The cells 

 of the opposite moiety, by passing into the com- 

 missures. 4. The tubes of the white substance 

 of the opposite moiety, by following the same 

 course. 



Fig. 422. 



LONGITUDINAL SECTION THROUGH 

 CERVICAL ENLARGEMENT OF SPINAL 

 CORD OF CAT. 



AC, Inferior white columns ; Ac', por- 

 tion showins the arrangement of 

 the longitudinal fibres ; PC, pos- 

 terior white columns ; G, grey sub- 

 stance between them (the vesicles 

 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 

 passing obliquely downwards, 

 across the grey substance, into the 

 anterior columus ; the second, 6, 

 traversing the posterior columns 

 horizontally, and then losing them- 

 selves in the grey substance ; the 

 third, c, for the most part becoming 

 continuous with the longitudinal 

 fibres of the posterior column ; all, 

 or ne:irly all, ultimately entering 

 the grey substance. 



