378 NORMAL HISTOLOGY AND ORGANOGRAPHY. 



deuce of this fact is experimental and positive. A 

 nerve fiber detached from its cell body dies. In 

 this way tracts will degenerate in the cord, some 

 above and some below a transverse cut. The em- 

 bryological evidence rests on equally positive facts. 

 In development certain tracts acquire medullary 



Postero-lateral horn. Posterior fissure. 



A nterior 

 horn. 



Lowenthal's 

 tract. 



Anterior root of spinal nerve. Anterior fissure. 



Fig. 267. Cross section of the spinal cord, lumbar region, i, zona 

 terminalis; 2, zona reticularis; 3, substantia gelatinosa of Rolando; 4, 

 stellate cells of posterior horn; 5, column of Clarke; 6, Waldeyer's cen- 

 tral cell column; 7, cells of lateral horn; 8, central canal; 9, antero- 

 mesial cells; 10, postero-mesial cells; n, antero-lateral cells; 12, postero- 

 lateral cells. 



sheaths earlier than others. This fact has greatly 

 extended our knowledge of the white matter in the 

 cord. The pathological evidence is a third factor. 

 Certain diseases produce degenerate lesions in the 

 cord. Proper interpretations of these lesions have 

 enabled us to map out definite nefve tracts in the 

 cord, and to determine their relations as well as pos- 



