700 



THE NERVOUS SYSTEM. 



the gray matter ; and (3) fibres leaving the gray matter, and pursuing a longer or 

 shorter horizontal course between the bundles of longitudinal fibres, with which 

 many of them are continuous. 



The investigation of pathological lesions has shown that of the main columns 

 of the cord each consists of certain sub-columns or tracts of fibres, for it has been 

 found that separate lesions are strictly limited to certain well-determined parts of 

 the organ without involving neighboring regions. That these parts or fasciculi 

 correspond to so many distinct anatomical systems, each endowed with special 

 functions, seems abundantly proved by the researches of Flechsig and others on 

 the development of the cord during the later periods of utero-gestation and in the 

 newly-born infant. Thus, on either side of the anterior median fissure a portion 

 of the antero-lateral column is divided off us the direct pyramidal tract (fasciculus 



FIG. 407. Columns of the cord. 



Atitr. Medn. Fitsure. 



FIG. 408. Transverse section of the gray substance of 

 the spinal cord, near the middle of the dorsal region. Mag- 

 nified 13 diameters. 



of Turck), which can be traced to be continuous with the non-decussating fibres 

 of the pyramid of the medulla. The remainder of the antero-lateral column of 

 the cord is formed of six tracts or columns, which, as to actual size, may be 

 divided into three large and three small tracts. The three former are : (1) The 

 crossed pyramidal tract, whose fibres when traced upward form the decussating 

 portion ' f the pyramid of the medulla oblongata ; (2) the direct cerebellar tract, 

 which passes above into the restiform body of the medulla ; (3) the antero-lateral 

 ground bundle, the fibres of which are continued into the formatio reticularis of 

 the medulla. The three latter are : (1) The antero-lateral descending cerebellar 

 tract (Loewenthal); (2) the antero-lateral ascending cerebellar tract (Gowers); (3) 

 the tract if Lissauer. For the prolongations of the first two, see Structure of 

 the Medulla. The last is not apparently found in the medulla. All these small 

 tracts occupy the surface of the cord (see Fig. 407). 



The posterior column of the cord is divided into two : the portion which lies 

 next the posterior median fissure is called the column of Goll (postero-median), 

 and if traced upward is found to be continuous with the funiculus gracilis of the 

 medulla. The remainder of the posterior column is called the postero-lateral or 

 Eurdach's column, and is prolonged into the medulla under the name of funiculus 

 cuneatus. 



Collateral Fibres. The posterior nerve-roots, on entering the cord, separate 

 into the component fibres, each of which bifurcates into an ascending and descend- 

 ing branch, which run upward and downward in the posterior column and in the 

 posterior cornu. Furthermore, each of these fibres before bifurcating and each 

 of its bifurcations gives off at intervals collateral branches, which penetrate the 



