5H THE NERVOUS SYSTEM. 



chiefly, first, to the divergence, enlargement, and decussa- 

 tion of the several columns, as they pass to be connected 

 with the cerebellum of the cerebrum ; and secondly, to the 

 insertion of new quantities of grey matter in the olivary 

 bodies and other parts, in adaptation to the higher office 

 and wider range of influence which the medulla oblongata 

 as a nervous centre exercises. 



Functions of the Medulla Oblongata. 



In its functions the medulla oblongata differs from the 

 spinal cord chiefly in the importance and extent of the 

 actions that it governs. Like the cord, it may be regarded 

 first, as conducting impressions, in which office it has a 

 wider extent of function than any other part of the nervous 

 system, since it is obvious that all impressions passing to 

 and fro between the brain and the spinal cord and all 

 nerves arising below the pons, must be transmitted through 

 it. The decussation of part of the fibres of the anterior 

 pyramids of the medulla oblongata explains the pheno- 

 mena of cross-paralysis, as it is termed, i.e., of the loss of 

 motion in cerebral apoplexy, being always on the side 

 opposite to that on which the effusion of blood has taken 

 place. Looking only to the anatomy of the medulla 

 oblongata, it was not possible to explain why the loss of 

 sensation also is on the side opposite the injury or disease 

 of the brain: for there is no evidence of a decussation 

 of posterior fibres like that which ensues among the 

 anterior fibres of the medulla oblongata. But the dis- 

 coveries of Brown-Sequard have shown that the crossing 

 of sensitive impressions occurs in the spinal cord (see 

 p. 498). 



The functions of the medulla oblongata as a nerve centre 

 seem to be more immediately important to the maintenance 

 of life than those of any other part of the nervous system, 

 since from it alone, or in chief measure, appears to be 



