520 



THE MEDULLA OBLONGATA. 



Fig. 352. 



nerve is succeeded by a third in the same line, which is connected with the nervus 

 vagus, and is also placed to the outer side of that for the hypoglossus. Further out, 

 a fourth nucleus begins to be observed, belonging to the glosso-pharyngeal nerve. 

 The last change in the arrangement of these small grey masses consists in the gradual 



narrowing of the nucleus of the par va- 

 gum, and the approximation of those for 

 the hypoglossal and glosso-pharyngeal 

 nerves which were previously separated 

 by it. 



Fig. 352. MAGNIFIED VIEWS OF TRANS- 

 VERSE SECTIONS OF THE MEDULLA OB- 

 LONGATA (after Lockhart Clarke, and 

 Reichert). f 



These figures are to be looked upon as in 

 part diagrammatic, no attempt having been 

 made to represent the natural difference of 

 colour in the parts. For the most part, 

 however, the grey substance is'indicated by 

 the smoother dark shading, and the white 

 substance by distinct lines. 



A, represents a section made at the 

 lower part of the decussation of the pyra- 

 mids; B, one immediately below the 

 olivary bodies ; C, one a very short dis- 

 tance below the calamus scriptorius ; and 

 D, a section in the lower part of the fourth 

 ventricle. The references are the following 

 in all the four figures : 



p, anterior pyramids ; p', their decussa- 

 tion ; 0, olivary bodies ; 0', the radiating 

 fibres proceeding from their interior; r, 

 restiform bodies and their nucleus ; pp, 

 posterior pyramids ; R, raphe ; c, central 

 canal and substance surrounding it ; tr, 

 grey tubercle of Rolando ; /, anterior 

 median fissure ; fp t posterior median 

 fissure ; a, arciform fibres ; I, lateral 

 column ; Z', larger cells and vesicular tract 

 of the lateral column ; CI a, anterior roots 

 of the first cervical nerve ; CI p, posterior 

 roots ; XII, hypoglossal nerve-roots issuing 

 at the side of the pyramid ; XII', its 

 nucleus ; XI, XI', spinal accessory nerve 

 and its nucleus ; VIII', nucleus of the 

 auditory nerve according to Reichert. 



In A and B, the decussation of the pyra- 

 mids is represented ; in A, the anterior 

 and posterior cornua of the grey matter 

 still exist as in the spinal cord ; in B, the 

 anterior cornua are much diminished in 

 size, the posterior have begun to pass 

 outwards, and to be converted into the 

 grey tubercles, and the intermediate nuclei 

 to make their appearance between them ; 

 in C, the central canal is wider and ap- 

 proaches the posterior aspect, and the 

 olivary body appears between the anterior 

 pyramid and the lateral column ; in D, the 

 canal is opened up in the fourth ventricle, 

 and the various grey nuclei are for the 

 most part in the vicinity of its floor. 



C. 



a- 



Langenbeck and Forg maintain that the pail regarded by Stilling as the nucleus 



