188 



THE ESSENTIALS OF HISTOLOGY 



to the crossed pyramidal tract, and consists of large fibres which pass 

 up into the cerebellum (direct cerebellar tract, c.t.). 



v. 



FIG. 223. DIAGRAMMATIC SEC- 

 TIONS OF THE SPINAL CORD AT 

 DIFFERENT PARTS, TO SHOW THE 

 CHIEF LOCALISED TRACTS OF 

 FIBRES IN THE WHITE SUB- 

 STANCE. (One and a half times 

 the natural size.) 



/. at the level of the sixth cervical 

 nerve ; //. of the third dorsal ; ///. 

 of the sixth dorsal; IV. of the 

 twelfth dorsal ; V. at the level of the 

 fourth lumbar, d.p.t, direct or an- 

 terior pyramidal tracts ; c.p.t. crossed 

 or lateral pyramidal tracts ; c.t. direct 

 cerebellar tract ; g, tract of Goll. 



d.p.t. 



The course of the nerve-tracts in the spinal cord, and in other parts 

 of the central nervous system, can best be made out by the study of 

 sections of the foetal cord, for it is found that the development of the 

 medullary substance occurs sooner in some tracts than in others, so that 

 it is easy to make out the distinction between them. Another method 

 consists in investigating the course which is pursued by degenerations 

 of the nerve-fibres in consequence of lesions produced accidentally or 

 purposely. 



Disposition of the nerve-cells in the grey matter. The nerve-cells 

 which are scattered through the grey matter are in part disposed into 

 definite groups. Thus there is a group of large niultipolar nerve-cells 

 in the anterior cornu ; their axis-cylinder processes pass out into the 

 anterior nerve-roots (column of the anterior cornu, fig. 221, a, b, c). In 

 the middle dorsal region there is a well-marked group of large rounded 



