MEDULLA OBLONGATA 



505 



It is arranged in the form of a capsule, which is open at its upper and 

 inner part, and has its sides corrugated or plicated, so as to give 

 the indented ajDpearance to a section. This capsule is, moreover, sur- 

 rounded with white matter externally, and through its open part white 

 fibres pass into or issue from its interior, and connect it with other 

 parts of the brain. It contains small, round and stellate cells, lying in 

 a gelatinous substance and among the fibres which pass through it. 

 A separate grey lamina above it, of similar structure, has been termed 

 the accessory olivary nucleus. 



The external fibres of the anterior columns of the cord, which at 

 the decussation of the pyramids are thrown outwards, are continued 

 upwards, on the surface of the medulla oblongata, and then pass, partly 

 on the outside of, and partly beneath the olivary bodies — being joined 

 in their further progress by the fibres issuing from the olivary nucleus. 

 To these fibres the term olivary fasciculus (fig. 356, o) has been 

 applied. 



The restiform bodies (figs. 354 and 355, d), placed behind and to the 

 outer side of the olivary bodies, are two lateral rounded eminences or 

 columns directly continuous with the posterior, and with part of the 

 antero-lateral colimms of the cord ; they diverge slightly as they ascend, 

 and thus occasion the greater width of the medulla at its upper part. 

 Each of them passes into the corresponding hemisphere of the cerebellum, 

 and constitutes its inferior peduncle. At first they are in contact with 

 the small tracts of the medulla, named the posterior pyramids ; but 

 higher up they become free and prominent, and assist in forming the 

 lateral boundaries of the fourth ventricle. There is a considerable 

 quantity of grey matter in their interior. 



By far the larger portion of the white substance of the restiform 

 body consists of longitudinal fibres, which include all those belonging 



Fig. 355. — View of the Posterior Surface of Fig. 355. 



THE Poxs Varolii, Corfora Quadrigemina, 

 AND Medulla Oblongata. 



a, a, the upper pair of corpora quadrigemina ; 

 '), b, tlie inferior ; /, /, superior peduncles of tlie 

 cerebellum ; c, eminence connected with the nucleus 

 of the hypoglossal nerve ; outside e is the external 

 auditoiynucleus ; beneath e and i, that of the vagus 

 nerve ; d, d, restiform bodies ; 2^, I>, posterior 

 pyramids ; r, v, groove in the middle of the fourth 

 ventricle, ending below in the calamus scripto- 

 rius ; 7, 7, roots of the auditory nerves. (See also 

 Fig. 358.) 



to the posterior column of the cord except 

 the posterior median column, some de- 

 rived from the lateral column, and also 

 a small band from the anterior column. 

 This last-named band runs obliquely 

 below the olivary body, and, as was shown 

 by Solly, connects the anterior column 

 with the cerebellum. 



The posterior pyramids (fasciculi graciles) (fig. 355, 2^ p) of the 

 medulla oblongata, the smallest of the four pairs of columns into which 

 it is divided, are situated one on each side of the posterior median 



