THE SPINAL CORD. 499 



the cortex of the cerebral hemisphere of the same side. The terminal 

 filaments of these fibers or axons are in physiologic relation either directly 

 or indirectly through intercalated neuron cells with the dendrites of the 

 cornual cells. When divided in any part of their course, these fibers undergo 

 descending degeneration. 



(b) The antero-lateral ground bundle or root zone. This tract lies external 

 to the pyramidal tract, surrounds the anterior horn of the gray matter, and 

 extends throughout the length of the cord. It is composed of short com- 

 missural or associative fibers which come from nerve-cells in the gray matter 

 from the same and opposite sides of the cord. After entering the white 

 matter they divide into two branches, pursue opposite directions, then re- 

 enter the gray matter at higher and lower levels and come into relation with 

 other nerve-cells: 



2. The lateral column, comprising that portion between the ventral 

 and dorsal roots, has been divided into: 



(a) The antero-lateral tract of Gowers. This tract is somewhat crescentic 

 in shape and situated on the lateral aspect of the cord external to the antero- 

 lateral root zone. It extends throughout the entire length of the cord. 

 When divided it undergoes ascending degeneration, which would indicate 

 that the axons originate in nerve-cells in the gray matter. This tract is 

 therefore probably afferent in function. 



The majority of the fibers composing this tract on reaching the pons 

 turn backward, pass through the superior medullary velum to terminate in 

 the dorsal vermis of the cerebellum. 



(b) The lateral limiting tract. This tract, which is quite narrow, lies 

 close to the external border of the gray matter. It is composed of fibers 

 which do not degenerate to any considerable extent after transverse section 

 and are in all probability associative fibers which come from nerve- cells in 

 the gray matter to re-enter at lower and higher levels. It is also believed by 

 some investigators that the anterior portion contains efferent and the pos- 

 terior portion afferent fibers; for this reason it is frequently termed the 

 mixed lateral tract. 



(c) The crossed pyramidal tract. This tract occupies the posterior por- 

 tion of the lateral column, though its exact position varies somewhat in 

 different regions of the cord. In the cervical and thoracic regions it is 

 covered by a layer of fibers. In the lumbar region, however, it comes to the 

 surface. From above downward this tract gradually diminishes in size, 

 for the reason that its fibers and their collaterals enter the gray matter at 

 successive levels. The terminal branches of these fibers are in close physi- 

 ologic relation either directly or indirectly through intercalated neuron 

 cells with the dendrites of the cornual cells. These fibers are the continua- 

 tions of fibers which take their origin in cells which are located in the cortex 

 of the cerebral hemispheres of the opposite side. When divided in any part 

 of their course, they undergo descending degeneration. They are therefore 

 efferent neurons and of the second order. 



(d) The direct cerebellar tract, or column of Flechsig. This tract is 

 situated on the surface of the lateral column external to the crossed pyramidal 

 tract. It slightly increases in size from below upward. It is composed of 

 fibers the cells of which are found on the inner side and base of the posterior 



