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NERVOUS SYSTEM. 



larged portion of the spinal cord, connecting the brain with the 

 cord below. The white substance is composed of the medullary 

 fibres connecting brain and cord, and the gray matter is arranged 

 variously between the bands of white fibres. It has an anterior 

 and a posterior fissure, corresponding to those of the lower portion 

 of the cord, and the central canal of the cord here opens into the 

 fourth ventricle. 



How do the columns of the cord arrange themselves in the 



medulla ? 



The medulla continues in a general way the arrangement of the 

 fibres in tracts of the cord below, but as the diameter is greater the 

 general shape is pyriform and the shape of the columns nearly pyra- 

 midal (Fig. 31). The anterior columns of the cord become the 



FIG. 31. 



Medulla Oblongata and Pons Varolii, anterior surface. 



anterior pyramids of the medulla ; the posterior columns, the resti- 

 form bodies, and the lateral columns correspond to the lateral tract 

 of the medulla with the olivary bodies. The fibres, however, do 

 not follow this arrangement so closely, but the columns of the cord 

 distribute themselves variously in the medulla. 



