' or '/'///; !//;/>//./.. i soi 



There are several small detached port ions of the olivary nucleus known as the ac- 

 cessory olivary nuclei. Tlic,-c an- named according to their position with refen 

 to the chief portion o: uiive proper. They are less corn ign ted than the chief nucleus, 

 and appear rod-like in sections. The largest is the iliir.tnl mn n.ti.ri/ nl/ lau. 



The inii/inl iiri-ixxorii ii/iniri/ ii/irliiiN is widt inferior end, which extends a 



little below the inferior extremity of the chief nucleus. The luti rcl ucrixxori/ utirari/ 



', i/.s is the smallest. In serial sections the acces.-ory nuclei arc found to be plates 

 of grey substance and usually continuous u it h one another. 



The olivary nuclei are mainly cerebellar connections. By both ascending and 

 descending fibres each cerebellar hemisphere is connected with the olivary nucleus 

 of the same and opposite sides. Tlie.se fibres necessarily pass between the cere- 

 bellum and t he olives by way of the rest iform body, and. in so doing, form an obliquely 

 coursing bundle in the lateral border of the medulla known as the cerebello-olivary 

 fibres (Kg. ;VJo). 



The arcuate fibres are referred to as internal and external, according as they 

 course dorsal or ventral to the inferior olivary nucleus. 



The internal arcuate fibres comprise fibres destined for both the cerebellum 

 and cerebrum, and also for the association of the tegmental grey substance of the 

 two sides in which they course. Certain of the fibres passing between one restiform 

 body (cerebellar hemisphere) and the olive of the opposite side course internal to the 

 olive of the same side, and thus form the ventral portion of the internal arcuate fibres. 



Fia. 596. RECONSTRUCTION OF THE INFERIOR OLIVARY NUCLEUS, DORSO-LATERAL SURFACE. 



(After Sabin.) 



As noted above, the internal arcuate fibres consist in greatest part of cerebro-afferent 

 fibres, arising from the cells of the nucleus funiculi gracilis and funiculi cuneati and 

 sweeping downwards and decussating to form the lemniscus of the opposite side. 

 However, all the fibres arising in these nuclei do not enter the lemniscus. A few of 

 them cross the mid-line with the internal arcuates, but pass on to enter the restiform 

 body (cerebellar hemisphere) of the opposite side. Some of these course ventrally 

 and, upon approaching the olive of the opposite side, are deflected around the ventral 

 side of both the olive and the pyramid, and thus pass to the restiform body as external 

 arcuate fibres also. Certain of the internal arcuate fibres arise from the cells of the 

 nuclei of termination of the cranial nerves and from small cells situated in the grey 

 substance of the reticular formation. These, in crossing the mid-line, correspond 

 to the white commissures of the spinal cord. Some of them terminate in the med- 

 ulla; others join the lemniscus and pass towards the cerebrum; others reach the 

 cerebellar hemisphere of the opposite side. 



The external arcuate fibres, in addition to those mentioned above, comprise cer- 

 tain fibres which arise in the nuclei funiculi gracilis and cuneati and pursue a dorso- 

 lateral course to enter the restiform body of the same side. These form the dorsal 

 segment of the external arcuates. The greater mass of the external arcuates are 

 cerebello-olivary fibres. Certain of those passing from one olive to the restiform body 

 of the opposite side arc deflected at the raphe. and course on the ventral side of both 

 the other olive and the pyramid in order to reach the cerebello-olivary bundle. Like- 



t) 1 



