PEBIPHEHAL-NEEVE HOOTS, SPINAL GANGLIA, SPINAL COED. 



349 



upper extremities. It must not be suspected that the portions of the pos- 

 terior columns named contain all the fibers of a posterior root. Many fibers, 

 immediately after entering "the cord, gain the gray matter, while others 

 bend in their course, to pass through the posterior columns. Therefore 

 there lie in the upper sections of The cord relatively few of those fibers in 

 the posterior columns which entered lower down. Experimentally this has 

 been proved by following up the cord from a divided dorsal root, when the 

 degenerating portion of the cord grows smaller and smaller as one ascends. 

 At the same time the degenerated field approaches more nearly the median 

 line. 



In the highest part of the cord the funiculus cuneatus contains fibers 

 which do not come direct from the dorsal roots. Their origin is uncertain. 



A part of the posterior-root fibers extends to the vicinity of Clarke's 

 column of cells and there arborizes (Fig. 237). From this column of cells 



Fig. 225. 



Fig. 226. 



Section through the cervical and lumbar cord, with approximately-drawn 

 boundaries of the different divisions of the white matter. Arranged from em- 

 bryological principles, mainly from preparations with secondary degenera- 

 tion of one or more of the tracts, la, Crossed pyramidal tract. 1, Direct py- 

 ramidal tract. 2, Antero-lateral ground-bundle. 3, Tractus cerebello-spinalia 

 ventralis. 4, Tractus cerebello-spinalis dorsalis. 5, Lateral marginal zone. 6, 

 Postero-lateral, or Burdach'Sj column. 7. Postero-median, or Goll's, column. 

 8, Radicular zone. 9^ Ventral field of the posterior column. 



arises another tract of fibers. After section of the cord this tract degenerates 

 upward. It is the peripheral portion of the lateral column (4 in Fig. 235). 

 This tract may be followed to its entrance in the vermis of the cerebellum, 

 and is called the tractus cerebello-spinalis dorsalis. We are particularly in- 

 debted to embryological research (Flechsig) for our knowledge of this, the 

 direct cerebellar tract, and for our ability to distinguish it from the other 

 lateral tracts. In the first few weeks post-partum, when the pyramidal tract 



