THE COUBSE OF THE FIBERS IN THE SPINAL COED. 357 



relations of the spinal-eord tracts, the phenomena revealed by physiologic ex- 

 periments are to be very carefully interpreted; but, on the other hand, it seems to 

 me desirable that new examinations of spinal-cord sections, whether partial or total, 

 be made in man, because, with the lower animals, there ds reaction only to the coarsest 

 kind of impressions, which do not amount to actual pain. It is positively known, 

 so far, that the posterior columns do not conduct those impressions which in the 

 cortex are recognized as tactile, and it is quite probable that these are farther con- 

 ducted by the portion entering into the gray matter, which there soon connects with 

 its secondary extension. With these fibers must also be found the central paths 

 conveying impulses of temperature and pressure sensations. 



In the posterior columns run, presumably, tracts which, partly through their 

 cerebellar connections and partly through their cerebral connections with the so- 

 called cortical motor centers, in some manner influence the sensory regulation of 

 movements and muscle-tone. 



There remains still to be considered that part of the posterior root 

 whose fibers arborize around the cells of Clarke's column. It has probably 

 nothing to do with the conduction of tactile impressions, according to path- 

 ological data. The secondary tract, or prolongation upward from Clarke's 

 Column, does not join with the general sensory paths. From these cells arise 

 fibers which leave the gray matter laterally, and on the periphery of the 

 gray matter enter the direct cerebellar tract. AVith it they pass up to the 

 cerebellum. These fibers are doubtless important for the co-ordination of 

 movements. For not only in cerebellar disease are gait and station ineo- 

 ordinated, but also in tabes dorsalis, in which one meets with ataxia of the 

 highest degree, are these fibers of the posterior column and the columna 

 vesicularis degenerated, resulting in an interruption to the paths leading 

 to the cerebellum. 



The anatomical relations, then, which are affected by the entrance of 

 the posterior nerve-roots into the cord, are much more complicated than are 

 those of the anterior roots. We have already seen this to a degree. Prob- 

 ably there exist still other, as yet unknown, systems of fibers. 



The relations of many of the cells of the ventral and dorsal horns to the 

 root-fibers we have already learned. There are, in the gray matter, still 

 many cells, which do not, however, stand in direct relation to the root-fibers. 

 First, there are cells whose axis-cylinders do not pass over into a longitudinal 

 bundle or into a root-fiber, but soon after their source form extremely fine 

 arborizations. They are seen everywhere on the cross-section, but are espe- 

 cially noteworthy in the border-region of the dorsal horn. Then there have 

 been recognized multipolar, scattered cells, which give off one axis-cylinder 

 in the corresponding or the opposite antero-lateral tract (Figs. 210 and 237). 

 There it splits into an ascending and a descending branch (Fig. 220). The 

 branches from these "tract-cells" extend a short distance in the antero- 

 lateral columns, then give off collaterals, which again enter the gray matter 

 and tliere arborize around other cells. These cells unite by their processes 



