STRUCTUEE OF THE SPINAL COED. 221 



distinct in the cervical and dorsal regions. Here it lies external to the 

 crossed pyramidal tract, and consists of large fibres which are derived 

 from the cells of Clarke's column (fig. 252,/) and pass up into the cere- 

 bellum (dorso-lateral or cerebellar tract). The other one, situated more 

 anteriorly, lies in front of the crossed pyramidal and direct cerebellar^ 

 tracts in the lumbar region ; while in the dorsal and cervical regions it 

 forms also a narrow band of fibres curving round close to the external 

 surface of the cord, and extending even into the anterior column. This 

 is the antero-lateral ascending tract of Gowers. Its fibres are intermingled 

 with those of another tract (antero-lateral descending), which degenerates 

 (after section of the cord) below the section, and was first described by 

 Loewenthal. Both this and the ascending tracts are connected with the 

 cerebellum ; the tract of Gowers passing to that organ over and along 

 with the superior cerebellar peduncle, whilst the dorso-lateral and the 

 descending enter with the inferior peduncle. Lastly, there are two or 

 three other small tracts of fibres, some of which degenerate above a section 

 of the cord, others below. One of these, an ascending tract (i.e. under- 

 going degeneration above the point of section), is marked M in the 

 figures. This is the marginal bundle, and is formed by the fine fibres 

 of the posterior roots (Lissauer). Another, placed in the postero-lateral 

 column, is the so-called comma tract, degenerating for a few centi- 

 meters below the point of section. Other small portions of the 

 posterior columns which are marked in the figure (fig. 252, P.M'. and 

 s.P.-L.) are differentiated by the method of Flechsig, but their function 

 is not known. 



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

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

 definite groups. Thus there are two or three groups of large multi- 

 polar nerve-cells in the anterior cornu; their axis-cylinder processes 

 mostly pass out into the anterior nerve-roots (cells of the anterior cornu, 

 fig. 252, a, b, c). A well-marked group of large rounded nerve-cells, 

 best marked in the thoracic region, lies at the base of the posterior 

 cornu (Clarke's column, fig. 252, /). The cells of Clarke's column send their 

 axis-cylinder processes into the direct cerebellar tract. Another group 

 is seen on the outer side of the grey matter lying in a projection which 

 is sometimes known as the lateral cornu (intermedio-lateral tract, fig. 252, 



FIG. 252. SECTIONS OF HUMAN SPINAL COED FROM THE LOWER CERVICAL (A), MID- 

 DORSAL (B), AND MID-LUMBAR (C) REGIONS, SHOWING THE PRINCIPAL GROUPS OF 

 NERVE-CELLS, AND ON THE RIGHT SIDE OF EACH SECTION THE CONDUCTING TRACTS 



AS THEY OCCUR IN THE SEVERAL REGIONS. (Magnified about 7 diameters.) 



a, b, c, groups of cells of the anterior horn ; d, cells of the lateral horn ; e, middle group of 

 cells; /, cells of Clarke's column; g, cells of posterior horn; c.c., central canal; a.c, 

 anterior commissure. 



