FIBER TRACTS OF THE SPINAL CORD 105 



The Conduction of Sensations of Pain, of Heat, and of Cold. It is well estab- 

 lished on the basis of clinical observations that the paths for sensations of heat 

 and cold follow closely those for pain. They pass through the gray matter im- 

 mediately after entering the cord, cross to the opposite side, and ascend in the 

 lateral spinothalamic tract. 



According to May (1906) "it is clear that there are distinct and separate 

 paths for the impulses of pain, of heat, or of cold in the spinal cord, and that 

 these different and specific qualities of sensation may be dissociated in an affec- 

 tion of the spinal cord." That is, one of these forms of sensibility may be lost, 

 although the other two are retained. "But as these paths are anatomically 

 very closely associated from origin to termination these three forms of sensa- 

 tion are usually affected to a like degree." 



From what has been said above it will be apparent that the paths, mediating 

 pain and temperature sensibility, cross promptly to the opposite side of the 

 cord and ascend in the lateral spinothalamic tract. The path for touch crosses 

 more gradually, but finally comes to lie in the ventral spinothalamic tract of 

 the opposite side; while the sensory impulses from the muscles, joints, and 

 tendons, as well as some elements of tactile sensibility, are carried upward on 

 the same side of the cord by the long ascending branches of the dorsal root fibers, 

 which terminate in the nuclei of the funiculus gracilis and the funiculus cuneatus. 

 The connections established within the brain by the fibers of these various paths 

 cannot profitably be discussed at this point, but will be considered in Chapter XIX. 



Other afferent paths besides those already mentioned exist in the spinal 

 cord. These include the spino-olivary and spinotectal tracts (Fig. 78). The 

 former consists of fibers which arise from cells in the posterior gray column, 

 cross to the opposite side of the cord, and ascend in the ventral funiculus, to 

 end in the inferior olivary nucleus of the medulla oblongata. The spinotectal 

 tract consists of fibers which arise from cells in the posterior gray column and 

 which, after crossing, ascend in the lateral funiculus in company with those of 

 the lateral spinothalamic path to end in the roof (tectum) of the mesencephalon, 

 i. e., in the corpora quadrigemina. 



ASCENDING AND DESCENDING DEGENERATION OF THE SPINAL CORD 



When as a result of an injury a nerve-fiber is divided, that part which is 



severed from its cell of origin degenerates, while the part still connected with 



that cell usually remains intact. This is known as Wallerian degeneration, and, 



as will be readily understood, gives valuable information concerning the course 



