CH. XLII.] 



GllEY MATTER OF THE CORD 



611 



axis vertical. Ifc lies at the base of the posterior horn, and is best 

 marked in the thoracic region. Their axons pass into the direct 

 cerebellar tract. 



(3) Intermedia-lateral group. This is seen in the outer part of 

 tho <rmy matter of the lateral horn, and is most distinct in the upper 

 thoracic and lower cervical regions. 



(4) The middle cell column lies in the 'middle of tho crescent. 



(5) The cells of the posterior horn are usually small; they are 

 numerous, but are not disposed in special groups. 



Columns and tracts in the white matter of the spinal cord. Tho 

 columns of tho white matter which are marked 

 out by the points from which the nerve-roots 

 issue, are called the anterior, the lateral, and 

 the posterior columns ; the posterior is further 

 divided by a septum of the pia mater into 

 two almost equal parts, constituting the postero- 

 external column, or column of Burdach, and the 

 postero-median, or column of Goll (fig. 449). 

 In addition to these columns, however, it has 

 been shown that the white matter can be still 

 further subdivided. Those tracts in the white 

 matter perform different functions in the con- 

 duction of impulses. 



The methods of observation are the follow- 

 ing: 



(a) The einbryological method. It has been 

 found by examining tho spinal cord at different 

 stages of its development that certain groups 

 of the nerve-fibres put on their myelin sheath 



at earlier periods than others, and that the different groups of fibres 

 can therefore be traced in various directions. This is also known 

 as the method of Flechsig. 



(b) Wallerian or degeneration method. This method depends upon 

 the fact that if a nerve-fibre is separated from its nerve-cell, it wastes 

 or degenerates. It consists in tracing the course of tracts of 

 degenerated fibres, which result from an injury to any part of the 

 central nervous system. When fibres degenerate below a lesion, the 

 tract is said to be of descending degeneration, and when the fibres 

 degenerate in the opposite direction, the tract is one of ascending 

 degeneration. By the modern methods employed in staining the 

 central nervous system, it has proved comparatively easy to distinguish 

 degenerated parts in sections of the cord and of other portions of the 

 central nervous system. Degenerated fibres have a different staining 

 reaction when the sections are stained by what are called Weigert's 

 and Pal's methods; this consists in subjecting them to a special 



Fio. 447. Section of half tho 

 spinal cord to show the 

 principal groups of colls in 

 the grey matter ; o, groups 

 of cells in the anterior 

 horn ; c, Clarke's column ; 

 i, intormedio- lateral group ; 

 m, middle cell column ; i>, 

 scattered cells of the pos- 

 terior horn. (Diagrammatic 

 after Schiifer.) 



