292 NORMAL HISTOLOGY. 



as nerve-fibres, these being especially the cells of the anterior 

 horn, which are prolonged into the large motor nerves. 



FIG. 326. 



Diagram illustrating the probable relations between the celis and the fibres and the principal tracts 

 of the spinal cord ; the left half of the figure exhibits the communications of the several varieties of 

 nerve-cells : A, P, anterior and posterior cornua of gray matter ; PR, posterior root-bundles ; DP, 

 direct pyramidal tract ; CP, crossed pyramidal tract ; DC, direct cerebellar path ; GB, Gowers's 

 tract ; a, motor cells passing directly into fibres of anterior roots of spinal nerves ; b, various cells of 

 the antero-lateral column, including elements of Clarke's column (b'} and of substantia Rolandi ; 

 some give off collateral branches of remarkable size ; c, commissural cells ; d, cells to posterior 

 column ; e, Golgi cells of posterior horn. The right half of the diagram shows the communications 

 established by means of the collateral fibres. (After Lenhossik.) 



The posterior root-fibres are afferent processes of the nerve-cells 

 situated within the spinal ganglia. On gaining the posterior columns 

 of the cord, the sensory fibres divide into ascending and descending 

 branches, from which collateral twigs are given off at various levels. 

 The collaterals, after a longer or shorter course, pass horizontally 

 into the gray matter, and terminate, in the majority of cases, in 

 arborizations closely related to the nerve-cells of the posterior horn. 

 These latter cells supply the links of communication between the 

 sensory and motor roots, thereby establishing the paths for spinal 

 reflexes. In some cases the sensory fibres traverse the gray matter 

 and end directly in relation to the cells of the anterior horn. While 

 many of the cells of the posterior horn are confined to the gray mat- 

 ter, others send their nerve-processes into the surrounding white 

 matter to form particular tracts of nerve-fibres. 



