54 THE MEDULLA OBLONGATA AND PONS VAROLII. 



At the fourth ventricle the hypoglossal nucleus lies a short distance from the surface 

 covered by a flattened bundle of longitudinally running white fibres, which gives this 

 mesial triangle of the calamus scriptorius (trigonum hypoglossi) a white appearance. 



nX't 



C.r. 



ruam. 



Fig. 46. SECTION OF THE MEDULLA OBLONGATA 



AT ABOUT THE MIDDLE OF THE OLIVARY 



BODY. (Schwalbe. ) f 



f.l.a., anterior median fissure ;^ n.ar., nu- 

 cleus arciformis; 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 arciform 

 fibres; n.l. , nucleus lateralis ; a., arciform fibres 

 passing towards restiform body partly through 

 the substantia gelatinosa, (>., partly superficial to 

 the ascending root of the 5th nerve, a. V. ; X. , 

 bundle of vagus root, emerging ; f.r., formatio 

 reticularis ; c.r., corpus restiforme, beginning 

 to be formed, chiefly by arciform fibres, superfi- 

 cial and deep; n.c., nucleus cuneatus ; n.g., 

 nucleus gracilis ; t, attachment of the ligula ; 

 f.s., funiculus solitarius ; n.X., n.X'., two 

 parts of the vagus nucleus ; n.XIL, hypoglossal 

 nucleus; n.t., nucleus of the funiculus teres; 

 n.am., nucleus ambiguus ; r., raphe ; A., con- 

 tinuation of anterior column of cord ; o', o , 

 accessory olivary nuclei ; p.o.L, pedunculus olivse. 



Nearer to the surface of the floor and nearer also to the median groove is a small 

 group of cells, known sometimes as the nucleus of the funiculus teres (fig. 46, 

 n.t.). The cells are small and appear to give origin to fibres which belong to the 

 vago-glossopharyngeal roots. 



Vili 



Fig. 47. TRANSVERSE SECTION OF THE UPPER PART OF THE MEDULLA OBLONGATA. (Schwalbe.) 



py., pyramid ; o., olivary nucleus ; V.a., ascending root of the fifth nerve ; V11I., root of the 

 auditory nerve, formed of two parts, a. and b., which enclose the restiform body, c.r. ; n, VIII. p., 

 principal (dorsal) nucleus of the auditory nerve; n.VIII.ac.. accessory nucleus; g, ganglion cells 

 in the root ; n.f.t., nucleus of the funiculus teres ; n.XIL, nucleus of the hypoglossal; r., raphe. 



At the base of the posterior horn in the lower part of the bulb, and near the 

 centra canal, a group of cells (fig. 43, n. XI.} is seen in section, which if traced up- 

 wards is found to be pushed to the side as the central canal opens, so that in the 



