THE STRUCTURE OF THE BRAIN STEM 



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right round the medulla. Some fibres pass into the restiform body of the 

 same side. A larger number, forming the superficial arcuate fibres, pass 

 superficially to the olive to join the restiform body of the opposite side, 

 while others, the deep arcuate fibres, pass deeply to the olives, and crossing 

 in the median raphe turn upwards in. the broken mass of grey and white 

 matter which lies between the olives and the superficial grey matter of the 



01. Fibres 



FIG. ]84. Diagram to show the sources of the fibres making up the restiform body. 



Ar.N. arcuate nucleus ; Ar fibres, arcuate fibres ; Pyr, pyramid ; C.Sp. 

 Tract, direct cerebellar tract ; C.01 fibres, cerebello-olivary fibres ; Pl.B, 

 posterior longitudinal bundle ; DN, nucleus of Deiters ; NB, nucleus of Bech- 

 terew ; Ro.N, roof nuclei ; Vest. N, vestibular nerve. 



fourth ventricle. This decussation, which is known as the 'decussation 

 of the fillet ' or the sensory decussation, takes place immediately above the 

 level of the decussation of the pyramids. In its upward course it forms a 

 conspicuous strand of fibres, lying close to the mesial plane and separated 

 from its fellow of the opposite side simply by the median raphe. To this 

 collection of fibres is given the name of the filet or lemniscus. It is perhaps 



