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A MANUAL OF PHYSIOLOGY 



same and also on the opposite side), and the fact that it begins lower 

 down in the cord than the direct cerebellar tract is in favour of the 

 view that their cells of origin are not confined within exactly the 

 same boundaries. None of the fibres of the tract can come directly 

 from the posterior nerve-roots, since no degeneration is seen in it on 

 section of the roots alone. 



The antero-lateral ascending tract passes up through the medulla, 

 where some of its fibres perhaps form synapses with the cells of the 

 lateral nucleus, a collection of grey matter in the lateral portion of 

 the spinal bulb. But its main strand runs on unbroken through the 

 medulla, in front of the restiform body, and behind the olive, and 

 after reaching the upper part of the pons bends back through the 

 superior peduncle, to end in the worm of the cerebellum. 



Through the relay of the 

 gracile and cuneate nuclei, 

 the postero-internal and 

 postero-external columns 

 of the cord are further con- 

 nected on the one hand 

 with the cerebrum, and on 

 the other with the cere- 

 bellum. The cells of the 

 nuclei give off fibres (in- 

 ternal arcuate fibres) 

 which, sweeping in wide 

 arches across the mesial 

 raphe to the opposite side, 

 take up a position behind the pyramid in the fillet, a bundle 

 of fibres which becomes more compact, and therefore more 

 distinct as it passes brainwards. Receiving fibres from other 

 sources on its way, and also giving off fibres, it runs up- 

 wards into the dorsal or tegmental portion of the pons. 

 Here it divides into two portions, the mesial fillet and the 

 lateral fillet. The lateral fillet contains fibres arising in the 

 cochlear nucleus of the auditory nerve, and ends in the pos- 

 terior corpus quadrigeminum, and partly below the anterior 

 corpus quadrigeminum. It appears to be a path for the 

 conduction of auditory impulses. The mesial fillet contains 

 the fibres that come off from the gracile and cuneate nuclei. 

 Enlarged by the accession of fibres from the sensory nuclei 

 of the cranial nerves, it pursues its course through the 

 tegmentum of the crus, and terminates for the most part in 



FIG. 248 DIAGRAM OF DECUSSATION 

 OF FILLET. 



a, nucleus gracilis ; b, nucleus ctmeatus ; 

 c, internal arcuate fibres crossing the middle 

 line from a and b to the fillet d, and forming 

 the decussation of the fillet ; e, anterior 

 median fissure. 



