482 HANDBOOK OF PHYSIOLOGY. 



sions regarding the conduction of sensory and motor impressions through 

 the spinal cord. 



It is important to bear in mind that the gray matter of the cord, even 

 if it conduct some impressions giving rise to sensation, appears not to be 

 sensitive when it is directly stimulated. The explanation probably is, 

 that it possesses no apparatus such as exists at the peripheral terminations 

 of sensory nerves, for the reception of sensory impressions. 



The Conducting Paths in the Spinal Cord. 



a. Sensory Impressions are conveyed to the spinal cord by the pos- 

 terior nerve-roots, and generally speaking cross over to the opposite side, 

 and are conveyed upwards in two or three paths, according to the nature 

 of the sensory impulse. 



(1.) Sensibility to Pain is almost certainly conveyed upwards in that 

 part of the lateral column which is called by Gowers the antero-lateral 

 ascending tract (A L A T, Fig. 333). It is a tract of vertical fibres imme- 

 diately in front of the crossed pyramidal and direct cerebellar tracts. 

 The zone extends across the lateral column as a band which is largest in 

 area near the periphery of the cord, where it fills up the angle between 

 the crossed pyramidal and cerebellar tracts, and it reaches the surface 

 of the cord in front of the latter tract; it then extends forwards in the 

 periphery of the anterior column, almost to the anterior median fissure 

 (Gowers). 



(2.) Sensibility to Touch (tactile sensibility) is probably conveyed up- 

 wards, after decussating almost as soon as it enters the cord, in the pos- 

 terior median column. 



(3.) Sensibility of the Muscles (muscular sensibility). The path of 

 muscular sensation does not decussate, but passes upwards probably in 

 the posterior median column of the same side, passing up to it from the 

 hinder part of the postero-external column, and according to Elechsigin 

 the direct cerebellar tract. 



(4.) Sensibility to Temperature. The path for sensations of tem- 

 perature is probably near to that of sensibility to pain, in the lateral 

 column. 



(5.) Sensory Impressions subserving Reflex Actions. There is con- 

 siderable probability that all the paths for cutaneous sensibility undergo 

 interruption in the spinal cord, and do not pass straight up, as no ascend- 

 ing tract of degeneration has been demonstrated so far when a lesion has 

 been confined to the nerve-roots. If this be the <3ase, it is probable that 

 the same fibres which convey sensation have also to do with the cutaneous 

 reflexes. In the case of muscular reflexes, however, as the fibres pass 

 upwards without interruption, the reverse is in all probability the case, 



