460 THE NERVOUS SYSTEM. 
form the deep part of the restiform body and constitute its chief bulk. Streaming 
out from the hilum of the inferior olivary nucleus, they cross the mesial plane, and 
on the opposite side of the medulla they either pass through the inferior olivary 
nucleus of that side or sweep around it. Ultimately, on the dorsal aspect of the 
olivary nucleus, they are gathered together in the form of a conspicuous group of 
arcuate fibres, which curve backwards to take up a position in the deep part of the 
restiform body. In passing back, they traverse the spinal root of the trigeminal 
DESCENDING 
ROOT Vill. 
LIGULA 
FASCICULUS 
SOLITARIUS 
SPINAL \_ 
ROOT V. N 
\\ CEREBE\LLO -OLI vary, 
= 
XII. PYRAMID 
XII. 
[HYPOGLOSSAL] 
ARCUATE 
NUCLEUS 
Fic, 343.—DIAGRAM OF THE CEREBELLO-OLIVARY FIBRES. 
(This diagram has been constructed from the specimen figured on page 458.) 
N.X., Vago-glossopharyngeal nucleus. N.XII., Hypoglossal nucleus. 
nerve and break it up into several separate bundles. The cerebello-olivary fibres thus 
connect the inferior olivary nucleus of one side with the opposite side of the 
cerebellum. 
Although we have traced the cerebello-olivary fibres in an upward direction from the olive to 
the cerebellum, it is right to state that in all probability it is the great efferent tract of the 
inferior cerebellar peduncle. Its fibres are believed to arise in the cortex of the cerebellum 
(probably as the axons of the cells of Purkinje) and to descend in the inferior peduncle to estab- 
lish connexions with the cells of the olivary nucleus of the opposite side. The destination of the 
axons of the cells of the inferior olivary nucleus is not known with certainty, but Kolliker con- 
siders that they enter the lateral column of the cord. Whilst this may be regarded as the 
generally accepted view of the cerebello-olivary fibres, it is right to mention that Klimoff, in his 
recent work on the cerebellum, maintains that they are afferent in their function, and not 
efferent. 
Arcuate Nucleus (nucleus arcuatus),—lImnmediately above the decussation of 
the pyramids, a small flattened mass of gray matter, covered by superficial arcuate 
fibres, makes its appearance on the ventral or superficial aspect of the pyramid 
(Fig. 338). Ata higher level, when the open part of the medulla is reached, this 
gray mass shifts its position and comes to le upon the mesial aspect of the 
pyramid, and thus constitutes the immediate boundary of the antero-median 
fissure (Fig. 341). From its intimate connexion with the anterior superficial 
arcuate fibres, as they sweep out from the antero-median fissure, it receives the 
name of the arcuate nucleus. 
The nerve-cells which le in its midst are smaller than those of the inferior olivary nucleus, 
and are fusiform in shape. It would appear that large numbers of the anterior superficial arcuate 
fibres end in this nucleus, whilst others take origin within it. Many of the anterior arcuate 
fibres, however, sweep continuously over its surface and bind it down to the pyramid. At the 
upper end of the medulla the arcuate nucleus increases in size, and ultimately it becomes con- 
tinuous with the gray matter of the ventral part of the pons. 
