STRUCTURE OF THE MEDULLA OBLONGATA. 



583 



of these fibres emerge at the anterior median fissure, and form a band which 

 curves round the lower border of the olivary body, or passes transversely across 

 it and round the sides of the medulla, forming the arciform fibres of Eolando. 

 Others appear in the floor of the fourth ventricle, issuing from the posterior 

 median fissure, and form the white striae in that situation. 



Fig 327. The Columns of the Medulla Oblongata, and their connection with the Cerebrum 



and Cerebellum. 



Medulla, Oblongata 



Gray matter of the medulla oblongata. The gray matter of the medulla is a 

 continuation of that contained in the interior of the spinal cord, besides a series 

 of special deposits or nuclei. 



In the lower part of the medulla, the gray matter is arranged as in the cord, 

 but at the upper part it becomes more abundant, and is disposed with less appa- 

 rent regularity, becoming blended with all the white fibres, except the anterior 

 pyramids. The part corresponding to the transverse gray commissure of the 

 cord is exposed to view in the floor of the medulla oblongata, by the diverg- 

 ence of the restiform bodies, and posterior pyramids, becoming blended with 

 the ascending fibres of the lateral column, and thus forming the fasciculi teretes. 

 The lateral crescentic portions, but especially the posterior horns, become en- 

 larged, blend with the fibres of the restiform bodies, and form the tuberculo 

 cinereo of Rolando. 



Special deposits of gray matter are found both in the anterior and posterior 

 parts of the medulla. ; forming, in the former situation, the corpus dentatum 

 within the olivary body, and, in the latter, a series of special masses, or nuclei, 

 connected with the roots of origin of the spinal accessory, vagus, glosso-pharyn- 

 geal, and hypoglossal nerves. It thus appears that the closest analogy in struc- 

 ture, and also probably in general endowments, exists between the medulla 

 oblongata and the spinal cord. The larger size and peculiar form of the me- 

 dulla depends on the enlargement, divergence, and decussation of the various 

 columns ; and also on the addition of special deposits of gray matter in the 

 olivary bodies and other parts, evidently in adaptation to the more extended 

 range of function which this part of the cerebro-spinal axis possesses. 



