THE SPINAL CORD 555 



The antero-lateral columns are insensible, but are excitable both on 

 the surface and in their substance ; and direct stimulation of these 

 columns produces convulsive movements in certain muscles, which 

 movements are not reflex and are not attended with pain. The lateral 

 columns are less excitable than the anterior columns. 



The surface, at least, of the posterior columns is very sensitive, 

 especially near the posterior roots of the nerves. The deep portion^ 

 of the posterior columns are probably insensible except very near the 

 origin of the nerves. 



The above conclusions refer only to the general properties of dif- 

 ferent portions of the cord, as shown by direct stimulation, in the 

 same way that the general properties of the nerves in their course 

 are demonstrated. 



Motor Paths in the Cord. What has been said regarding the 

 direction of the fibres in the cord and the situation and course of the 

 degenerations following destruction of motor centres conveys a definite 

 idea of the motor paths in the cord. This idea is sustained by experi- 

 ments in which different columns of the cord have been divided in living 

 animals. 



The motor paths are in the direct pyramidal tracts (columns of 

 Tiirck) and in the crossed pyramidal tracts of the lateral columns. 

 The motor impulses are conveyed by the fibres of these tracts to the 

 multipolar cells in the anterior cornua of gray matter and are thence 

 transmitted to the anterior roots of certain spinal nerves. In the lower 

 dorsal region the conduction is confined to the crossed pyramidal tracts 

 in the lateral columns, while above, the direct pyramidal tracts partici- 

 pate in this action. 



The motor fibres decussate in the anterior pyramids of the bulb 

 (crossed pyramidal tracts), and in the cervical region to a compara- 

 tively slight extent, before the direct pyramidal tracts (columns of 

 Tiirck) pass to the encephalon. In the cervical region the decussn 

 tion takes place probably in the anterior white commissure. The f ac *'. 

 of this decussation of motor conductors is sustained by pathology 

 paralysis of motion following brain-lesions, occurring on the opposite 

 side of the body and by experiments in which the fibres as they 

 cross are divided by a longitudinal median section in the bulb and in 

 the cervical region of the cord. 



Vasomotor nerve-fibres exist in the lateral columns of the cord and 

 probably are connected with the cells of the gray matter. They pass 

 out in the anterior roots of the spinal nerves and go to the bloodvessels 

 either from the branches of the spinal nerves directly or through fila- 

 ments sent to the sympathetic. 



