808 THE SPINAL CORD. 



an end-station for some of the fibres of the vestibular nerve branches. 1 This 

 bulbo-spinal system is, at least in the main, uncrossed. It extends into the 

 lumbo-sacral region of the cord ; its fibres in their spinal course lie among those 

 of the periphery of the cord near the region of exit of the motor-root. Their 

 collaterals enter the anterior horn. y Some observers 3 conclude that this system 

 is derived from cerebellar cells. This can hardly be considered proven. There 

 is some evidence also of a quadrigemino-spinal system ; 4 this is mainly crossed, 

 the decussation occurring ventral to the central canal. The fibres pass back- 

 ward near the raphe of the reticular formation. In their spinal course they lie 

 among fibres of the ventral lip of the ventral column. The system extends to the 

 lumbo-sacral region of the cord. The cells of the red nucleus 5 also send, accord- 

 ing to some authorities, fibres into the spinal cord as far as the lumbar region. 

 This rubrospinal system is a crossed one, its fibres decussating in the roof of the 

 mesencephalon. The fibres in their spinal course lie in the central part of the 

 lateral column somewhat ventral to the main portion of the pyramidal fibres. 



Among the fibres passing tailward from the encephalon into the cord, those 

 forming the corticospinal system or pyramidal tracts are perhaps the best 

 known. Its fibres are branches from certain cells of the Rolandic cortex. 

 They descend through the internal capsule, pes pedunculi, and pedal longi- 

 tudinal fibres of the pons, and compose the ventral four-fifths and more of each 

 pyramid of the bulb. The decussation of the pyramids is the crossing in 

 bulk of the bundles of this tract at the caudal end of the bulb. The vast 

 majority of its fibres cross at this place and shift into the dorsal part of the 

 lateral column of the cord, lying separated (in man and most examined forms) 

 from the surface of the cord only by the fibres of the dorsal cerebellar tract. 

 Some of the crossed pyramidal fibres extend the whole length of the cord, 

 reaching the most distal coccygeal region. 7 In its course along the spinal cord 

 it diminishes, owing to the ending of the constituent fibres at various levels. 

 Its progressive decrease is far from regular, many fibres stopping short at some 

 regions, comparatively few in others. The decussation of the crossed part of 

 the system, especially in man, is not completed at the cephalic end of the cord, 

 but continues back for a variable distance along the cord. The fibres which 

 continue in the homonymous lip of the ventral spinal fissure before crossing 

 form what is called the ventral pyramidal bundle, or Tiirck's bundle, and in 

 man this has been seen extending even into the lowest sacral region. 8 v. 



1 Monakow, Arch.f. Psychiat., Berlin, 1883, Bd. xiv.; Ferrier and Turner, Phil. Trans., 

 London, 1894, vol. clxxxv. B. ; A. Thomas, Compt. rend. Soc. de biol., Paris, 1895, 1896 ; R. 

 Russell, Phil. Trans., London, 1895, vol. clxxxvi. p. 633; Teljatnik, Neurol. Centralbl., 

 Leipzig, 1897 ; R. E. Lloyd, Joum. Physiol., Cambridge and London, 1900, vol. xxv. p. 191. 



2 Sehafer, "Proc. Physiol. Soc., "Joum. Physiol., Cambridge and London, 1899, vol. xxiv. 



3 Marchi, Eiv. sper. di freniat., Reggio- Emilia, 1886, tomo xii.; 1887, tomo xiii. ; Atti 

 d. Accad., Firenze, 1891 ; Pelizzi, Riv. sper. di freniat., Reggio-Emilia, 1892; A. Thomas, 

 " Le Cervelet," Paris, 1897 ; Biedl, Neurol. Centralbl., Leipzig, 1895. 



4 H. Held, Neurol. Centralbl, Leipzig, 1890, S. 481 ; Arch. f. Physiol. / Leipzig, 1893, 

 S. 245; Boyce, Neurol. Centralbl., Leipzig, 1894, S. 466; Phil. Trans., London, 1895. 

 But Miinzer obtained no spinal degeneration after injury of anterior corpora quadrigemina 

 in the rabbit or bird, Prag. med. Wchnschr., 1895. 



5 H. Held, Neurol. Centralbl., Leipzig, 1890; Arch. f. Physiol., Leipzig, 1891; 

 Abhandl. d. k. Gesellsch, d. Wissensch., Leipzig, 1892, No. 6, Bd. xviii. ; Ramon y Cajal, 

 " Apuntos para el estudio, etc.," 1895 ; Kohnstamm, loc. cit. 



ff Not in Macacus. E. P. France, Phil. Trans., London, 1889; Sherrington, Joum. 

 Physiol., Cambridge and London, 1889, vol. x. 



7 Sherrington, ibid., 1889, vol. x. ; Boyce, Phil. Trans., London, 1894, p. 186 ; Dejerine 

 and Thomas, Arch, de physiol. norm, et path., Paris, 3 896, tome ii. Previous observers 

 found the tract end at the fourth lumbar level, cf. Tooth, "Spinal Degen.," London, 1890. 



8 Dejerine and Thomas, Arch, de physiol. norm, et path., Paris, 1896; it had been 

 traced by Tooth, op. cit., 1889, to the second lumbar segment. In the monkey I 

 have not with certainty found it farther back than the eighth cervical level ; Redlich, to 

 third cervical in the cat (Neurol. Centralbl., Leipzig, 1897). The actual level of the main 

 decussation seems subject to much individual variation (Flechsig, " Leitungsbahnen, etc.," 

 Leipzig, 1876). 



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