THE OLIVARY BODY. 



313 



giving origin to a bundle of fibres, which pass out laterally just 

 as does the pneumogastric lower down. This is the glosso- 

 pharyngeal nerve and root. Farther still from the median 

 line, in the floor of the fourth ventricle, is seen a group of 

 small cells, the commencement of the acoustic nucleus. Scat- 

 tered nerve-cells arising here pursue an obliquely forward and 

 outward direction, making the lower margin of the auditory 

 root. 



Transverse sections of the medulla just at the edge of the 

 pons bring the acoustic region into view ; the upper olivary 

 body is here visible. Behind this are scattered a few large cells, 

 from which fibres pass backward to form higher the facial root. 



Fio. 140. One-half transverse section of 

 the human medulla just below the edge of tho 

 pons, showing acoustic nucleus and roots which 

 enclose the inferior cerebellar peduncle I. 0. 

 P. : I, internal root ; E, external root ; M, up- 

 per olivary nucleus ; Lf , lower facial nucleus. 

 3 diains. 



FIG. 141. Diagram of a transverse 

 action just above the edge of the pona, 

 having the obliquity given it in Fig. 182, 

 6 & 7 : 6, abducens root ; 7, facial root. 

 For other explanations, see text. 



Occupying the floor of the fourth ventricle is a large mass of 

 gray matter, from which the acoustic arises. This gray matter 

 contains many small round and some multipolar cells. The 

 nerve has two roots, one internal, the other external. (See 

 Fig. 140.) The former arises from fibres emerging from the 

 raphe near the fourth ventricle and from the gray matter just 

 external to it, and pursues a course downward and forward 

 through the lateral white matter. This root, at its point of 

 emergence, is joined by fibres from the posterior root curving 

 Jaround the surface of the medulla, like, if not identical with, 

 the arciform fibres. The external root has also one origin from 

 the gray matter near the median line, and curving outward on 



