786 



DISSECTION OF THE BRAIN. 



Fibres of 

 lateral tract, 



Direct 



cerebellar 



tract. 



Fibres of 

 funiculus 



cuneattis, 

 gracilis, and 

 of Rolando. 



Formation 

 of restiform 

 body. 



The lateral tract is composed of the remaining fibres of the lateral 

 column of the cord, after the crossed pyramidal tract has been given 

 off. Most of these pass deeply behind the olivary body, and through 

 the reticular formation to the pons ; but one small band, the direct 

 cerebellar tract, is continued superficially from the lateral column to 

 the cerebellum. This band is often visible on the surface of tin 

 medulla, as a whiter streak lying along the outer edge of the lateral 



tract, and inclining backwards 

 above the tubercle of Rolando 

 to join the restiform body. 



Posterior funiculi. The 

 white fibres of the cuneate 

 and slender funiculi are the 

 continuation of the postero- 

 external and postero-median 

 columns of the cord respec- 

 tively, and are believed to end 

 entirely in the grey nuclei of 

 the funiculi. The funiculus ol 

 Rolando has only a very tnin 

 superficial white layer, which 

 is also derived from the pos- 

 terior column. 



The restiform body is formed 

 by the arciform fibres of the 

 medulla, by the direct cere- 

 bellar tract, by fibres from the 

 gracile and cuneate nuclei and 

 from the vestibular portion of 

 the auditory nerve. 



Dissection. The separated 



Arciform 

 fibres : 



superficial, 



FIG. 265. TRANSVERSE SECTION OF THE 

 MEDULLA OBLONGATA AT THE LOWER 

 PART OF THE FOURTH VENTRICLE 



(CLARKE). 



a. Pyramid. 



b. Olivary body. 



c. Tubercle of Rolando. 



d. Restiform body. 



e. Lateral boundary of fourth ventricle. 



f. White core of the olivary body, with 

 the roots of the hypoglossal nerve to its 

 inner side. 



g. Olivary peduncle. 



h. Deep arciform fibres entering the 

 raphc (a few more are added from a 

 second drawing). 



k.l. Reticular formation. 



n. Floor of fourth ventricle. 



o. Hypoglossal nucleus. 



p. Glosso-pharyngeal nucleus. 



r. Inner auditory nucleus. 



s. Superficial arciform fibres. 



t. Remains of the gelatinous substance. 



pons and medulla will now be 

 divided longitudinally. One 

 half we will put aside. On the 

 other, by making transverse 

 sections at different levels, the 

 student will be able to dis- 

 tinguish the grey matter of 

 the olivary body and a few 



other larger nuclei as well as 



the chief bundles of white fibres, but the parts described in small 

 type require specially stained sections for their proper display. 



Arciform fibres. In the upper half of the medulla oblongata, 

 covering its anterior surface and traversing its substance, is an 

 extensive system of fibres, curving outwards and backwards from 

 the median plane to the restiform body, to which this name has 

 been given. 



The superficial arciform fibres (fig. 265, s) have already been 

 noticed in the description of the exterior of the medulla oblongata. 



