INTERNAL STRUCTURE OF MEDULLA OBLONGATA AND PONS. 563 



REST! FORM 

 BODY 



.DORSAL EXT. 

 3CUATE FIB. 



RACILENUCL. 



CUNEATE NUCL. 



des of the medulla oblongata ; (3) external arcuate fibres coming from the arcuate 

 uclei; and (4) olivo-cerebeUar fibres. 



The fasciculus spinocerebellaris [posterior] extends upwards from the lateral funi- 

 ilus of the medulla spinalis. In the lateral district of the medulla oblongata it 

 ?cupies a similar position ; but before 

 le olive is reached it inclines back- 

 ards, crosses the posterior lateral 

 irrow and passes obliquely upwards 

 ito the restiform body. As its fibres 

 iverge backwards, they pass over and 

 over up the tractus spinalis of the tri- NUCL1 

 Bminal nerve and its nucleus, thus TRA TU T S R* 

 mtting them out from the surface, 

 he fibres of the fasciculus spinocere- 

 ellaris, in the first instance, enter 

 ito the lateral or superficial part of 

 ie restiform body. 



Bruce has shown that the fibres of the 

 )ino-cerebellar tract ultimately lie in the 

 intre of the restiform body, forming as it 

 , ere its central core, and that, in the cere- 

 ilium, they can be traced to the superior FlQ - 496. DIAGRAM, 

 Tmis. Which shows in part the fibres which enter into the 



constitution of the restiform body. 



The posterior external arcuate fibres 



ike origin from the gracile and cuneate nuclei, and enter the superficial part of 

 le restiform body of the same side. 



The anterior external arcuate fibres proceed from the inferior portions of the 

 .racile and cuneate nuclei of the opposite side. It can easily be determined that, 

 fter decussating in the median plane, all the internal arcuate fibres which arise 

 om these nuclei do not enter the lemniscus medialis. A large proportion of them 

 rain the surface by sweeping round the medial aspect of the pyramid in the 

 aterior median fissure. Many of them gain the surface by piercing the pyramid 

 : by passing out between it and the olive. These fibres constitute the anterior 



t.al arcuate group, and on the surface of the medulla oblongata they sweep 

 Fasciculus graciiis backwards around it, forming a 



Graciie nucleus thin i ayer over fa e olive and 

 luscuneatus^ / ,.. . ', , . . , .. 



^^aiMK^L ultimately reaching the restiform 



body. The anterior external 

 arcuate fibres, as well as the 

 spino - cerebellar tract - fibres, 

 cover over the tractus spinalis 

 of the trigeminal nerve, which 

 thus comes to take up a deeper 

 position in the substance of the 

 medulla oblongata (Figs. 495 

 and 496). 



The other elements in the 

 restiform body, viz., those de- 

 rived from the nucleus olivaris 

 inferior and the nuclei arcuati, 



Nucleus of tractus 

 pinalis n. trigemini 



us spinalis of 

 trigeminal nerve 



Fasciculus spino- 

 cerebellaris 



cerebro-spinal 

 fasciculus 



Central canal 

 Decussation of pyramids 



tuched anterior column of gray matter 



SECTION THROUGH THE JUNCTION BETWEEN THE 

 SPINAL MEDULLA AND MEDULLA OBLONGATA OF THE ORANG. 

 apino-cerebellar tract is well seen, especially on the right side, have already been described 



Thus, the restiform body 



veys to the cerebellum (1) fibres conveying impulses from the posterior spinal 



3 of the same and also from the opposite side of the medulla spinalis, the former 



P being interrupted in the nucleus dorsalis and the nucleus graciiis and nucleus 



s of the same side, the latter in the nucleus graciiis and nucleus cuneatus 



ie other side ; and (2) fibres from the olivary and arcuate nuclei, which convey 



from the higher regions of the brain, directly or indirectly (probably the 



ter) from the motor area of the cerebral cortex. 



37 a 



