348 ANATOMY OF THE CEXTEAL NERVOUS SYSTEM. 



entering posterior roots from the sensory nerves of the legs to the medulla 

 oblongata. 



Later it will be seen, that still other subdivisions must be made in the 

 posterior columns. 



The manner of propagation of diseases in them, particularly the results 

 of submitting fresh lesions of the cord to the Marehi process of staining, 

 which places the single degenerated medullary sheaths under the action of 

 a special reagent, has largely added to our knowledge of these tracts. 



That portion which closely adjoins the gray commissure {A in Fig. 223) 

 must contain a separate system of fibers, because, in tabes for example, it 



f 





Fig. 224. — Secondary degenerations, ascending and descending, after a transverse 

 lesion of the upper dorsal cord. (After Striimpell.) 



never participates in the disease, even when the remainder of the posterior 

 columns degenerates. It may be termed the ventral field of the posterior 

 columns. 



The posterior columns consist almost exclusively of fibers entering by 

 way of the posterior roots. These roots are so arranged that the entering 

 fibers lie always laterally, close up to the posterior horns, but that those 

 entering later, therefore higher in the cord, shove the more early arrived 

 fibers toward the median line. So it happens that in the cervical part of 

 the cord the fibers from the lower extremities occupy principally G-oll's 

 column, while the column of Burdach still contains many fibers from the 



