52 THE MEDULLA OBLONGATA AND PONS VAROLII. 



tively coarse network of grey matter containing nerve-cells, intersected by bundles of 

 white fibres ; but a small part, probably representing the lateral horn of the cord, and 

 like that containing numerous nerve-cells many of relatively large size, remains for a 

 time in the lateral column, near the surface, and is known as the nucleus lateralis 

 (fig. 43, .?.) 



Meanwhile the posterior horns have become gradually shifted laterally, simulta- 

 neously with an increase in size of the posterior columns of the medulla, so that in 

 place of forming an acute angle with the posterior median fissure, they now lie 

 almost at right angles to it (fig. 42). Moreover, the caput cornu enlarges and 



&.R. 



Fig. 44. TRANSVERSE SECTION OF THE MEDULLA OBLONGATA SOMEWHAT ABOVE THE MIDDLE OF THE 

 OLIVARY BODY. (E.A.S.) MAGNIFIED 5 DIAMETERS. ( From a photograph. ) 



p.l. b, posterior longitudinal bundle ; n.t, nucleus of funiculus teres ; n.XII, nucleus hypoglossi ; 

 n.X, nucleus vagi ; n'X, nucleus ambiguus ; s, fasciculus solitarius ; n.p, nucleus posterior (cuneatus) ; 

 f.r, formatio reticularis ; t, tsenia ; s.R, substantia Rolandi ; a. V, ascending root of fifth ; c.r, corpus 

 restiforme ; ar.int, internal arcuate fibres ; X, issuing root of vagus ; n.l, nucleus lateralis ; n', groups 

 of large cells, perhaps belonging to nucleus lateralis; a-l.tr, antero-lateral ascending tract; n.d.o, 

 nucleus dentatus olivse ; acc.o, accessory olivary nucleus; s. o, siliqua olivse ; k.o, hilum olivse ; p, 

 pyramid ; /, fillet ; r, raphe ; n.ar, nucleus of arcuate fibres ; ar.ext, external arcuate fibres. 



comes close to the surface, where it presently forms a distinct projection, the funiculus 

 of Rolando, which, a little higher up, swells into the tubercle of Rolando (fig. 42, .R.). 

 At the same time the cervix cornu diminishes in size and like the anterior cornu is 

 eventually broken up by the passage of transverse and longitudinal bundles of white 

 fibres through it, into a reticular formation, which then separates the caput cornu 

 posterioris (fig. 43, #.) from the rest of the grey matter, and joins the reticular for- 

 mation derived from the rest of the grey matter. In the tubercle of Rolando the 

 caput cornu is close to the surface, and its grey substance can readily be seen, but 

 above the tubercle it lies deeper, being covered by a well-marked bundle of white 

 fibres, the so-called ascending root of the fifth nerve (a. V.\ and by the oblique 

 arched fibres which are passing over it to form the restiform body. 



The fibres of the ascending trigeminal root have been supposed to take origin from the cells 

 of the tubercle of Rolando, but this is not the case, for firstly they do not grow from these 



