1894.] Degenerations in the Brain and Spinal Cord, fyc. 271 



Antero-lateral Columnar Fibres. Meynert's fibres (fountain decus- 

 sation) pass from the side of the lesion across the raphe immediately 

 ventral to the post. -longitudinal bundles, and turn vertically down, 

 lying in the raphe in front of the post, -longitudinal bundles. The 

 fibres can be traced into the antero -lateral column of the cord as far 

 as the lower cervical region. In their descent they move slightly 

 forwards, but they are always more anterior than the fibres of the 

 post.-longitudinal bundles. The degeneration method shows that 

 Meynert's fibres arise in a focus close to the point of commencement 

 of the descending root of the 5th, on a level with the roots of the 

 3rd nerves. The vast majority of the fibres decussate completely ; 

 the decussation is a very horizontal one. 



Lateral Columnar Fibres. In the highest segments these are 

 derived from fibres, -which decussate in front of the preceding group, 

 and originate from a slightly higher level in the tegmentum; they 

 probably correspond to Forel's decussating fountain fibres. In 

 the mesencephalon they occupy a position in front of and slightly 

 external to the antero-lateral columnar fibres ; lower down they are 

 more laterally situated, and in the pons and medulla form a well 

 defined group, immediately in front of the ascending root of the 5th 

 and the substantia gelatinosa, and dorsal to the nucleus lateralis ; 

 they are traversed by the root of the 7th, and are bounded externally 

 by trapezoid, and ascending cerebellar fibres. They are internal to 

 the lemniscus and quite distinct from it ; they can be traced to the 

 upper lumbar spinal cord. In the spinal cord they occupy a position 

 immediately in front and to the outer side of the pyramidal tract ; 

 they are readily distinguished from the latter by their large size. 



Degeneration of Descending Root of 5th. The Marchi method shows 

 that this root is invariably degenerate upon the side of the lesion. 

 It arises in the lateral aspect of the Syivian grey matter at about the 

 level of the upper oculo-motor nucleus, descends to meet the ascend- 

 ing root, and passes out without interruption. 



Pyramidal System. The degeneration is confined exclusively to 

 the pyramid on the side of the lesion, and the degeneration appears 

 complete. 



There is a slight bifurcation at the decussation, a small group of 

 fibres passing back to the lateral tract on the same side. There is 

 thus a direct lateral pyramidal tract, but there is no anterior direct 

 pyramidal tract. 



The decussation of the pyramid is not confined to the cervical 

 region ; degenerate fibres leave the pyramidal system from the in- 

 ternal capsule, the crusta, and from the pyramid in the medulla. A 

 large group passes through the thalamus and beneath the corpora 

 quadrigemina, many of the fibres crossing over in the roof of the 

 aqueduct. A considerable number of degenerate fibres pass back to 



VOL. LV. u 



