STRUCTURE OF THE MEDULLA OBLOXGATA. 511 



bodies ; and the lateral, continuous with the lateral columns 

 of the cord, are named simply from their position. On the 

 fibres of the lateral column of each side, near its upper 

 part, is a small oval mass containing grey matter, and 

 named the olivary body ; and at the posterior part of the 

 restiform column, immediately on each side of the posterior 

 median groove, a small tract is marked off by a slight 

 groove from the remainder of the restiform body, and called 

 the posterior pyramid. The restiform columns, instead of 

 remaining parallel with each other throughout the whole 

 of the medulla oblongata, diverge near its upper part, 

 and by thus diverging, lay open, so to speak, a space called 

 the fourth ventricle, the floor of which is formed by the 

 grey matter of the interior of the medulla, by this diverg- 

 ence exposed. 



On separating the anterior pyramids, and looking into 

 the groove between them, some decussating fibres can be 

 plainly seen. 



Distribution of the Fibres of the Medulla Oblongata. 



The anterior pyramid of each side, although mainly com- 

 posed of continuations of the fibres of the anterior columns 

 of the spinal cord, receives fibres from the lateral columns, 

 both of its own and the opposite side ; the latter fibres 

 forming almost entirely those decussating strands before 

 mentioned, which are seen in the groove between the 

 anterior pyramids. 



Thus composed, the anterior pyramidal fibres proceed- 

 ing onwards to the brain are distributed in the following 

 manner: I. The greater part pass on through the pons 

 to the cerebrum.-" A portion of the fibres, however, run- 



* The expressions " continuous fibres," and the like, appear to be 

 usually understood as meaning that certain primitive nerve-fibres pass 

 without interruption from one part to another. But such continuity 

 of primitive fibres through long distances in the nervous centres is 



