THE SPINAL CORD.— GENERAL. 



473 



divisions of the cord are by no means well established. It is 

 possible that vaso-motor, respiratory, and probably other kinds 

 of impulses, pass by portions of the lateral tracts other than 

 the crossed pyramidal. When a lateral half of the cord is 

 divided, the loss of function is not permanent in all instances, 

 but has been recovered from without any regeneration of the 

 divided fibers; and even when a section has been made higher 

 up on the opposite side, partial recovery has again followed ; 

 so that it would appear that impulses had pursued a zigzag 

 course in such cases. We do not think that such experiments 

 show that impulses do not usually follow a definite course, but 

 that the resources of nature are great, and that, when one tract 

 is not available, another is taken. 



It is plain that impulses do not in any case travel by one and 

 the same nerve-fiber throughout the cord, for the size of this 

 organ does not permit of such a view being entertained; at the 

 same time there is a relation between the size of a cross-section 

 of the cord at any one point and the number of nerves con- 

 nected with it at that region. 



We may attempt to trace the paths of impulses in a cord 

 somewhat as follows : 1. Volitional impulses decussate chiefly 



V TV III u I T IV m u I xir XI X ixviuvn vr v iv m u i viii vu vi v iv m H i 

 Sacral. Immhar. Dorsal. Cervteal. 



Pig. 337. — Diagram to illustrate relative and absolate extent of (I) gray matter, (3) 

 white columns in successive sectional areas of spinal cord, and (3) sectional areas 

 of several nerve-roots entering cord. iV"i?, nerve roots; AG, LC,PC, anterior, 

 lateral, posterior columns; Or, gray matter (after SchSfer, Ludwlg, and Woro- 

 schiloff). 



in the medulla oblongata, but also, to some extent, throughout 

 the whole length of the spinal cord. They travel in the lateral 

 columns (crossed pyramidal tracts chiefly, if not exclusively), 

 and eventually reach the anterior roots of the nerves through 

 the anterior gray cornua, passing to them, possibly, by the ante- 

 rior columns. From the cells of the anterior cornua, impulses 



