CHAPTER XXXV. 



THE MEDULLA OBLONGATA. 



The " oblong marrow " is the direct continuation of the spinal 

 marrow, and contains the different items in the construction of 

 the latter, prolonged upward and mingled with some additional 

 gray masses. The exact relationship of the different parts of the 

 medulla to those of the spinal cord may be best understood if we 

 suppose the latter, when it reaches its upper limit, to be split 

 vertically on its posterior side down to the central canal, and the 

 lateral masses so separated from one another that the central gray 

 part of the spinal cord becomes spread out on the posterior sur- 

 face of the medulla oblongata. The gray matter of the medulla 

 oblongata consists, then, of two portions distinct from each other ; 

 one being the direct continuation of the gray columns of the 

 spinal marrow, and the other being made up of certain gray 

 nodules imbedded here and there among the white strands. 

 These latter, as a rule, subserve special functions, while the con- 

 tinuation of the gray columns of the spinal cord, which are 

 spread out on the floor of the fourth ventricle, contains the nerve 

 cells that preside over the movements which are most important 

 for the every-day business of life. 



The functions of the medulla may be conveniently divided, in 

 the same manner as those of the cord, into its conducting power 

 and its use as a central nervous organ. 



THE MEDULLA OBLONGATA AS A CONDUCTOR. 

 The various columns of the spinal cord are so distributed in 

 the medulla that the anatomy of their course gives some indica- 

 tion of the channels by which impulses are carried through it. 

 But here, as in the spinal cord, we should remember that the 

 white fibres must be regarded as the direct and rapid means of 

 transit of impulses, while the felt work of fine fibres in the gray 

 part can also conduct impulses in all directions. Though the 



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