STRUCTURE OF THE MEDULLA OBLONGATA. 



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the strands of the hypoglossal nerve, while in a corresponding groove along its outer surface is 

 the line of exit of the vagus, glosso-pharyngeal, and spinal accessory nerves. It is covered on 

 its surface by longitudinal and arcuate fibres, while in its interior [it contains the dentate 

 nucleus. ] 



[The functions of the olivary bodies are quite unknown, but it is important to remember 

 that they are connected by fibres with the dentate nuclei of the cerebellum. Fibres pass into 

 the olivary body from the posterior column of the cord of the opposite side, and it is also con- 

 nected with the dentate body of the opposite side, while, as we know, the dentate body is 

 connected with the tegmentum, so that through the left dentate body of the opposite side, the 

 tegmentum of, say, the right cms, is connected with the right olivary body (Gowers).] 



[Decussation of the pyramids is the term given to those fibres which cross obliquely in 

 several bundles, at the lower part of the medulla, from the anterior pyramid of the medulla 



nam. 



Fig. 465. Fig. 466. 



Fig. 465. Section of the medulla oblongata at the so-called upper decussation of the pyramids. 

 fla, anterior, sip, posterior median fissure ; nXI, nucleus of the accessorius vagi ; 11XII, 

 nucleus of the hypoglossal ; da, the so-called superior or anterior decussation of the pyra- 

 mids ; py, anterior pyramid ; n.ar, nucleus arciformis ; 0\ median parolivary body ; 0, 

 beginning of the nucleus of the olivary body ; oil, nucleus of the lateral column ; Fr, 

 formatio reticularis ; g, substantia gelatinosa, with {aV) the ascending root of the trige- 

 minus ; 71c, nucleus of the funiculus cuneatus ; nc x , external nucleus of the funiculus 

 cuneatus ; ng, nucleus of the funiculus gracilis (or clava) ; H l , funiculus gracilis ; H 2 , 

 funiculus cuneatus ; cc, central canal ; fa, fa 1 , fa 2 , external arciform fibres x 4. Fig. 466. 

 Section of the medulla oblongata through the olivary body. nXII, nucleus of the hypo- 

 glossal ; nX, nX 1 , more or less cellular parts of the nucleus of the vagus ; XII, hypoglossal 

 nerve; X, vagus; n.am, nucleus ambiguus ; til, nucleus lateralis; 0, olivary nucleus; 

 oal, external, and oam, internal parolivary body ; fs, the round bundle, or funiculus soli- 

 tarius ; Or, restiform body ; p, anterior pyramid, surrounded by arciform fibres ; fae, pol, 

 fibres proceeding from the olive to the raphe (pedunculus olivee) ; r, raphe, x 4. 



into the lateral column of the cord of the opposite side (fig. 464, d) to form its lateral pyramid 

 tracts, or crossed pyramidal tracts. The number of fibres which decussate varies, and in some 

 cases all the fibres may cross.] 



[The grey matter of the medulla is largely a continuation of that of the cord, although it is 

 arranged differently. As the fibres from the lateral column of the cord pass over to form part 

 of the anterior pyramid of the medulla on the opposite side, they traverse the grey matter, and 

 thus cut off the tip of the anterior cornu, which is also pushed backwards by the olivary body, 

 and exists as a distinct mass, the nucleus lateralis (fig. 465, nl). Part of the anterior grey 

 matter also appears in the floor of the 4th ventricle as the eminence of the fasciculus teres, and 

 from part of it springs the hypoglossal nerve (fig. 466, XII). The neck joining the modified 

 anterior and posterior cornua is much broken up by the passage of longitudinal and transverse 



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