THE MEDULLA OBLONGATA 



105 



(n.c.), and of the tubercle of Eolando (g}. The anterior or mesial area 

 is occupied in front by the pyramid (p), and behind this by a reticular 

 formation (reticularis alba, A) composed of longitudinally coursing 

 bundles of fibres interlaced with fibres that are passing obliquely from 

 the opposite side, through the raphe, towards the restiform body (fig. 

 229, r.a.). The middle area, which lies between the issuing bundles 

 of the two sets of nerve-roots, consists in its deeper part of a similar 



XI I. r.fi. 



FIG. 229. PART OF THE RETICULAR FORMATION OF THE MEDULLA OBLONGATA. 



r.a. reticularis alba ; r.g. reticularis grisea ; between them a root-bundle of the hypoglossus 

 ( XII.). The longitudinal fibres of the reticular formation are cut across ; the transversely 

 coursing fibres are internal arcuate fibres, passing on the right of the figure towards the 

 raphe. 



reticular formation (fig. 228, fr), but with more grey matter and 

 nerve-cells (reticularis grisea, fig. 229, r.g.} Superficially there is 

 developed within it a peculiar wavy lamina of grey matter containing a 

 large number of small nerve-cells ; this is the nucleus of the olivary 

 body (fig. 228, o). 



The floor of the fourth ventric le is covered by a layer of ciliated 

 epithelium-cells, continuous below with those lining the central canal, 

 and above, through the Sylvian aqueduct, with the epithelium of the 



o2 



