THE SPINAL CORD. 449 



missural 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. 



(c) The antero-lateral tract of Marchi and Lowenthal. This 

 tract is situated at the inner and anterior angle of the anterior column. 

 After removal of the one-half of the cerebellum it degenerates down- 

 ward. 



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 anterior root zone. It extends throughout the entire 

 length of the cord. When divided it undergoes ascending degenera- 

 tion, which would indicate that the axons originate in nerve-cells 

 in the gray matter. This tract is therefore afferent in function. 



(b) The lateral limiting tract. This tract^wrnch 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 and are 

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

 the gray matter to re-enter at lower and higher levels. 



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

 portion of the lateral column, though its exact position varies some- 

 what 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 physiologic relation with the 

 dendrites of the cornual cells. The cells of these axons are located 

 in the cortex of the cerebral hemispheres of the opposite side. When 

 divided in any part of their course, they undergo descending de- 

 generation. , 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 horn (Clark's vesicular column). From 

 this origin the fibers pass obliquely outward to the surface and then 

 directly upward to terminate, as its name implies, in the cerebellum. 

 Decussation of these fibers takes place in the superior vermiform lobe 

 of the cerebellum. When divided this tract degenerates upward. It 

 is therefore in all probability an afferent tract and of the second order. 



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