536 THE NEKVOUS SYSTEM 



PATH "IV." The fourth and last division of the dorsal root 

 fibres follows a somewhat more uncertain course. The neuraxes of 

 its peripheral neurones end in arborizations about the many small 

 cells in the dorsal horns of the spinal cord, on the same, and possi- 

 bly also to some extent on the opposite side. Thence they pass up 

 the spinal cord by neurones of higher orders, which form associa- 

 tion bundles in the lateral columns and thus connect the dorsal 

 horn cells of successively higher levels. In the brain these paths 

 have been traced into the formatio reticularis. 



A considerable number of dorsal horn cells in the spinal cord 

 send their neuraxes into a narrow superficial zone in the anterior half 

 of the lateral column to form the ventro-lateral ascending column or 

 tract of Gowers. This tract, increasing in size, continues up the 

 spinal cord to the lateral column of the medulla oblongata. Its 

 further course is somewhat uncertain, though it undoubtedly con- 

 tinues upward through the lateral portion of the formatio reticu- 

 laris in the pons, where some of its fibres turn sharply backward 

 and enter the vermis cerebelli through the middle, and possibly 

 also the superior, cerebellar peduncles ; other fibres continue up- 

 ward through the formatio reticularis to the optic thalamus 

 (Hoche*). From this point its impulses probably reach the cor- 

 tex of the cerebral hemisphere after the same manner and in com- 

 pany with the fibres of the preceding division (PATH " III "). 



C. The Association Paths 



Besides the motor and sensory paths of the central nervous sys- 

 tem there are certain other tracts which connect the nuclei of vari- 

 ous levels. Some of these are tracts of ascending, some of descend- 

 ing degeneration. Many of them, however, contain both ascending 

 and descending fibres and may be called mixed fibre tracts. 



Some of the above tracts contain long fibres, e. g., the sulco- 

 marginal fasciculus, while others, e. g., the antero-lateral ground 

 bundles of the spinal cord, consist chiefly of short fibres. The 

 course of many of these association fibres is so difficult to follow 

 that they are not yet well known. We shall only attempt, there- 

 fore, to trace briefly the course of the more important fasciculi, 

 first those of the spinal cord and later those of the brain. 



The comma tract of Schultze in the middle root zone of the pos- 

 terior white column has already been mentioned as probably con- 



* Arch. f. Psychiat., 1896. 



