CliAPTEE XXIII. 



The Medulla Oblokgata. 



At the upper end of the spinal cord the white fibers of which it is made 

 up are disposed in various ways, the extent and form of the gray matter 

 changes considerably, new deposits of neuroglia and of ganglion-cells appear, 

 and the well-known picture of the cross-section of the spinal cord rapidly 

 disappears; especially is it indistinct when, at the upper segment of the cord, 

 right and left, there where the lateral tracts were, the inferior olive arises, — 

 a gray, much folded, richly cellular layer, — and when the central canal, 



ecru. I . 



Fig. 230. — Section through the upper cervical cord. Hinterhorn, Posterior 

 horn. Proc. reticularis, Association-field. Seitenhorn, Lateral horn. Rad. ant. 

 N. cerv. I, Ant. root of I cervical nerve. 



approaching more and more nearly to the dorsal surface, expands into the 

 fourth ventricle. 



The series of transverse sections here presented is intended to explain 

 the evolution of the medulla oblongata out of the spinal cord. 



Fig. 330 represents a section of the cervical cord, corresponding to that 

 part from which passes the first cervical nerve. It but recalls the relations 

 as already described in the preceding chapter. Three points, however, dis- 

 tinguish it. The first is the peculiar form of the posterior horn, which is 



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