STRUCTURE OF THE MEDULLA OBLONGATA. 



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partly appearing on the surface as a smooth, olive-shaped eminence (fig. 262). It 

 consists, externally, of white substance ; and, internally, of a gray nucleus, the 

 corpus dentatum. The gray matter is arranged in the form of a hollow capsule, 

 open at its upper and inner part, and presenting a zig-zag or dentated outline. 

 White fibres pass into or from the interior of this body, by the aperture in the 

 posterior part of the capsule. They join with those fibres of the anterior column 

 which ascend on the outer side, and beneath the olive, to form the olivary fasci- 

 culus, which ascends to the cerebrum. 



Fig. 2G3. The Columns of the Medulla Oblongata, and their Connection with the 

 Cerebrum and Cerebellum. 



Medulla Oblonyata 



The restiform body is formed chiefly of fibres from the posterior column of the 

 cord ; but it receives some from the lateral column, and a fasciculus from the 

 anterior, and is continued, upwards, to the cerebrum and cerebellum. On entering 

 the pons, it divides into two fasciculi, above the point of the fourth ventricle. 

 The most external one enters the cerebellum ; the inner one joins the posterior 

 pyramid, is continued up along the fourth ventricle, and, joining the fasciculi 

 teretes, passes up to the cerebrum. 



Septum of the 'medulla oblongata. Above the decussation of the anterior 

 pyramids, numerous white fibres extend, from behind forwards, in the median 

 line, forming a septum, which subdivides the medulla into two lateral halves. 

 Some 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 strias in that situation. 



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

 continuation of that contained in the interior of the spinal cojd, 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 

 apparent 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 



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