518 



THE MEDULLA OBLONGATA. 



Course of fibres from the spinal cord upwards through the medulla 

 oblongata. Assuming, for convenience of description, the existence of three 

 white columns of the cord, these are disposed as follows. 



1. The posterior column, with the exception of the fasciculus gracilis, is 

 distinguished by the name of processus cuneatus and enters into the forma- 

 tion of the restifonn body, which ascends to the cerebellum. The fasciculus 

 gracilis ascends to the cerebrum. 



2. The lateral column ascends towards the base of the olivary body, and 

 is disposed of in three ways ; (1,) some of its fibres from the surface and 

 deep part join the restiform body and proceed with it to the cerebellum ; 

 (2,) a larger number, passing obliquely inwards, then come forwards between 

 the anterior columns, and crossing the median plane appear as the fibres of 

 decussation, and form the chief part of the opposite anterior pyramid ; (3,) 

 the remaining fibres pass up to the cerebrum, as the fasciculi teretes 



Fig. 351. Fig. 351. DIAGRAMMATIC REPRESENTA- 



TION OP THE PASSAGE OF THE COLUMNS 

 OP THE MEDULLA OBLONGATA UPWARDS 

 AND DOWNWARDS. 



A, the specimen, which, is seen from 

 before, includes the medulla oblongata and 

 the pons Varolii, with a small portion of 

 the spinal marrow. The left lateral column 

 (that to the reader's right) has been lifted 

 out of its place to the side, and the ante- 

 rior and posterior columns of that side 

 remain undisturbed : the right anterior and 

 posterior columns have been removed, and 

 the lateral column remains in its place. 

 The upper part of the right pyramid is 

 removed. The transverse fibres of the pons 

 Varolii have been divided in circumscribed 

 portions to different depths corresponding 

 with the several places of passage of the 

 columns of the medulla. 



P, pons Varolii, part of the anterior sur- 

 face, where it has been left entire ; p, the 

 right and left pyramids, the upper part of 

 the right has been cut away ; p', the fibres 

 of the left pyramid as they ascend through 

 the poris exposed by the removal of the 

 superficial transverse fibres ; p'', placed on 



the deeper transverse fibres of the pons on the right side, close below the divided fibres 

 of the pyramid ; a, left anterior column of the cord, passing upwards into the undecus- 

 sated part of the anterior pyramid, and into a', the olivary column ; 0, olivary body ; 

 o', the continuation of the olivary column ascending deeply through the pons, and 

 exposed by the removal of a small portion of the deeper transverse fibres; o", the 

 same fibres divided by a deeper incision on the right side ; I, the right lateral column, 

 passing upwards into the following parts, viz., x, the deeper part passing by decussation 

 into the left pyramid ; r, the part passing into the restiform body ; ft, the part ascending 

 in the back of the fourth ventricle as fasciculus teres ; to the outer side of this are seen 

 the ascending fibres of the posterior pyramid ; I', the left lateral column drawn aside 

 from its place in the spinal cord ; the fasciculus teres, ft, and the part to the restiform 

 body, r, cut short ; x , the deeper part passing by decussation into the right pyramid ; 

 r', the part of the restiform body derived from the anterior column of the spinal cord ; 

 pc, the posterior column of the left side exposed by the removal of the lateral column, 

 and shown ascending to the restiform body as fasciculus cuneatus, fc : on the right side 

 the posterior column being removed, fc, points to this fasciculus cuneatus cut short 

 below. 



B, explanatory outline of the section of the spinal cord, a, anterior columns ; p, 

 posterior; I, lateral. 



