CH. XL VI.] 



SECTIONS OF THE BULB 



669 



anterior cornu of the cord) ; the lower part of the grey matter of the 

 olivary body (o, o'), and most anteriorly the pyramid (py). 



Third section. This (fig. 412) is taken at about the middle of 

 the olivary body, and passes also through the lower part of the floor 

 of the fourth ventricle. The central canal has now opened out into 

 the fourth ventricle, and the grey matter on its floor contains the 

 nuclei of the twelfth and tenth nerves ; bundles of the fibres of these 

 nerves course through the substance of the bulb, leaving it at the 

 places indicated in the diagram. 



n.c 



FIG. 412. Section of the medulla oblongata at about the middle of the olivary body, f.l.a., Anterior 

 median fissure; n.ar., nucleus arcuatus; p, pyramid; XII., bundle of hypoglossal nerve emerging 

 from the surface; at b, it is seen coursing between the pyramid and the olivary nucleus, o; f.a.e., 

 external arcuate fibres ; n.L, nucleus lateralis ; a., arcuate fibres passing towards restiform body, 

 partly through the substantia gelatinosa, g,, partly superficial to the descending root of the fifth 

 nerve, d.V. ; X., bundle of vagus root emerging; f.r., formatio reticularis ; C.r., corpus restiforme, 

 beginning to be formed, chiefly by arcuate fibres, superficial and deep ; n.c., nucleus cuneatus ; n.g., 

 nucleus gracilis; <, attachment of the ligula; /.s., funiculus solitarius; n.X., n.X.', two parts of 

 the vagus nucleus; n.XII., hypoglossal nucleus; .., nucleus of the funiculus teres; n.am., 

 nucleus ambiguus; r., raphe; A., continuation of the anterior column of cord; o', o", accessory 

 olivary nucleus; p.o.l., pedunculus olivse. (Modified from Schwalbe.) 



The nucleus gracilis and nucleus cuneatus are pushed into a more 

 lateral position, and higher up are replaced by small masses of grey 

 matter mingled with nerve-fibres (nucleus posterior) ; the restiform 

 body (C.r.) now forms a well-marked prominence, and the olivary 

 body is well seen with its dentate nucleus ; from the open mouth of 

 this corrugated layer of grey matter a large number of fibres issue, 

 and passing through the raphe, course as internal arcuate fibres to 

 the opposite restiform body, and thus to the cerebellum ; some pass 

 to the restiform body of the same side; the continuation of the 



