THE CENTRAL NERVOUS SYSTEM. 



2 9 I 



laterally into the white matter and constitute the nerve-fibres of the 

 direct cerebellar tract. 



The lateral horn when well developed, as in the intermedio- 

 lateral tract of the tho- 

 also con- 



of small, 



.._ _., .._ ^^T~ 



p^T 



'% 



^tU " 



FIG. 325. 



racc regon, 

 tains groups 

 frequently bipolar, cells 

 (2030 JJL) which re- 

 semble the isolated cells 

 of the posterior cornu. 



In addition to the 

 groups of nerve - cells 

 described, isolated clus- 

 ters of "outlying" 

 ganglion - cells exist 

 beyond the gray sub- 

 stance, within the white 

 matter of the antero- 

 lateral and posterior 

 columns. 



The composition 

 of the gray matter is 

 very intricate, including 

 as it does not only 

 nerve-fibres of various 

 sizes, both medullated 

 and non - medullated, 

 and countless fibrils of 

 varying thickness de- 



rived from the processes of the ganglion-cells, but also the universally 

 present substantia spongiosa, the modified neuroglia of the gray 

 matter, which contributes additional nuclei and fibrils of its own. 

 The recent advances in our knowledge concerning the processes of 

 nerve-cells have introduced new elements of complexity, for it must 

 be remembered that, in addition to the richly-branched protoplasmic 

 processes, the axis-cylinders contribute numerous fibrils both as the 

 collateral fibres and as the net-works of fine terminal fibres in 

 which the axis-cylinder processes of cells of the second type end. 



The relation between the various nerve-fibres and the cells of the 

 gray matter is a question of great difficulty ; the researches of Golgi, 

 Ram6n y Cajal, Kolliker, and others within the last few years have 

 established that the protoplasmic processes probably neither anas- 

 tomose with one another nor unite with nerve-fibres : likewise, 

 that the axis-cylinder processes of certain cells are directly continued 



jtb** 

 ^^ 



Portion ot anterior horn of gray matter of spinal cord of calf : 

 g, multipolar ganglion-cells lying within pericellular lymph- 

 spaces (/) ; r, r, bundles of nerve-fibres (f) passing from gray 

 matter to form anterior roots ; w, white matter ; /, portions of 

 isolated processes of nerve-cells ; n, larger processes in section ; 

 v, blood-vessel. 





