288 PHYSIOLOGY CHAP. 



along the different segments of the ventral grey matter. It is 

 probable that some at least of the collaterals of the direct 

 pyramidal tract decussate in the cord, and pass to the opposite 

 side through the ventral commissure, before they enter into 

 relation with the cells of the ventral roots. 



As shown by Fig. 174 the pyramidal fibres undergo a descend- 

 ing degeneration, but this never extends to the fibres of the 

 ventral roots so long as the cells of the ventral horn remain 

 intact. 



(&) Two bundles can be traced from the lateral column to the 

 cerebellum : one, described by Marchi, undergoes descending 

 degeneration after extirpation of the same side of the cerebellum 

 (direct ventro-lateral cerebellar tract) ; the other, described by 

 Flechsig, degenerates in the ascending direction, after lesions of 

 the lateral part of the cord (direct dorso- lateral cerebellar tract). 



The former, as shown by Fig. 176, occupies 

 in dogs the ventral three-fourths of the 

 ventro-lateral column, and also dips in- 

 wards in front of the crossed pyramidal 

 tracts. [More recent investigations have 

 proved that it does not take origin in 

 the cerebellum, but from cells of the brain- 

 stem that lie immediately ventral to it, 

 FIG. i7(3.-section of spinal cord and chiefly from Belter's nucleus. ED.] 

 (lumbar region) of dog, killed The direct ascending cerebellar tract 



three months after removal of /f _. , , 



right half of cerebellum, (lig. 17o) is better known ; it lies in 

 hdo7s m ' 1; the dorsal margin of the lateral column, 



and increases in size as it ascends, till on 

 reaching the sides of the bulb it passes through the restiform 

 body to the median lobe of the cerebellum. 



The fibres of Flechsig's cerebellar tract originate from the cells 

 of Clarke's column on the same side, and therefore degenerate 

 upwards. 



(c) Gowers identified another important tract, which occupies 

 an irregular area in the lateral column in front of the direct cere- 

 bellar tract and the crossed pyramidal tract, and is known as the 

 ventro-lateral ascending bundle (Fig. 177). This tract grows larger 

 as it ascends ; it can be followed into the bulb and pons Yarolii. 

 After lesions of the lumbar segments it undergoes ascending 

 degeneration. Its cells of origin are probably in the dorsal horn. 

 We shall return to the significance of this bundle in considering 

 the effects of partial transverse section of the cord. 



(d) Each dorsal column contains two bundles, which are 

 separated anatomically by a septum from the 'middle of the 

 thoracic region upwards : the funiculus gracilis or column of Goll 

 occupies the medial dorsal part, and the funiculus cuneatus or 

 tract of Burdach the lateral part of the column. We have 



