806 THE SPINAL CORD. 



tract," similarly intact in tabes, and a long descending tract noted by Hoche, 

 the septo - marginal of Bruce and Muir ; the tract found by Wiener and 

 Miinzer ascending but of intraspinal origin.) Some of the descending fibres 

 extend through seven and even twelve segments of the cord. Cajal has noted 

 column cells contributing fibres to the dorsal columns. As a rule the long 

 fibres are of larger diameter than the short. 



Some of the mediate cells give off axons which cross from one lateral half 

 of the cord to the other, while others do not. The former seem to be quite 

 numerous, 1 and their main passage of crossing to lie in the ventral white 

 commissure. The median ventral cell group of the ventral horn of grey matter 

 is probably a group of these mediate cells.' 2 Some mediate cells have been 

 described as giving a bifurcating axon, one stem from which crosses the 

 median sagittal plane, whereas the other does not. The number of mediate 

 cells appears to be very great, affording a basis, therefore, for very various 

 possibilities of direction of conduction in the cord. But it is impossible at 

 present to say Avhether the majority of the mediate cells belong to the 

 intrinsic (simply spinal) system, or to the spino-encephalic system, which is 

 certainly very large. 



2. Extrinsic mediate systems. — (a) Spino-encephalic. — (i.) Spino- 

 cerebellar. — Some intraspinal cells possess branches which extend headwards into 

 the superior vermis of the cerebellum. One set of these forms an uncrossed 

 spino-cerebellar system, the axons of which ascend in the dorsal part of the 

 margin of the lateral column and in the restiform body. These cells of 

 origin exist perhaps throughout the whole length of the cord, but are most 

 numerous along the region between the first thoracic segment and the second 

 lumbar (man). There the cells lie grouped together, forming the vesicular 

 column of Clarke. 3 A small subgroup, probably belonging to the same system, 

 lies in the upper cervical region, and as scattered cells in the lower brachial and 

 other segments. It is more doubtful whether the group in the sacral region 

 (Stilling's) is part of the system. Spinal lesions in the sacral region of man 

 do not cause degeneration of the dorsal cerebellar tract. There is some reason 

 to think that the lateral division of the nucleus cuneaius belongs to the same 

 system. 4 This system, called the dorso-lateral or restiformal spino-cerebellar, 

 is remarkably developed in man, and in the monkey more than in other 

 mammalian types examined, especially in its more posterior portion. Clarke's 

 column forms a nucleus of ending for collaterals from the afferent roots of the 

 lower limb, 5 and for the pyramidal tract. 6 



Another spino-cerebellar system, mainly crossed (heteromeric), lies in the 

 ventro-lateral edge of the lateral column. 7 The cell-bodies whence these fibres 



1 Cajal, van Gehuchten, v. Lenhossek, etc. 



2 v. Lenhossek, " Der feinere-Bau des Nervensystems," Aufl. 2, Leipzig, 1895. 



3 Fleclisig, " Leitungsbahnen im Gehirn u. Riickenniark," Leipzig, 1876; Singer, 

 Sitzungsb. d. k. Akacl. d. Wissensch., Wien, 1881, Bd. lxxxiii. S. 390; Lciwenthal, Bull. 

 Soc. vaudoise d. sc. not., Lausanne, 1885, tome xxi. p. 92; Mott, Brain, London, 1890, 

 vol. xiii. ; Tooth, "Spinal Degenerations," Loudon, 1889; A. W. Campbell, Liverpool 

 Med.-Chir. Journ., January 1894 ; Mott, Monatschr. f. Psychiat. u. Neurol., Berlin, 1897, 

 Bd. i. ; Laura, Arch. ital. de biol., Turin, 1882; Schiifer, "Proc. Physiol. Soc.," Journ. 

 Physiol., Cambridge and London, 1899, vol. xxiv. ; Lowenthal, Eec. zool. Suisse, 1886, tome 

 iv., and others. 



4 Sherrington, Journ. Physiol., Cambridge and London, 1892, vol. xvi. ; Alex. Bruce, 

 " Illust. of the Mid- and Hind-Brain," Edinburgh, 1892 ; A. Tschermak, Arch. f. Physiol., 

 Leipzig, 1898. 



5 Leyden, "Klin. d. Riickenmarks krankh.," Bd. ii. ; Lissauer, Fortschr. d. Med., Berlin, 

 1884 ; Arch./. Psychiat., Berlin, 1885, Bd. xii. S. 431 ; Krauss, Neurol. Ccntralbl., Leipzig, 

 1885, Bd. iv.; Hadden and Sherrington, Brain, London, 1888, vol. xi. ; J. Dejerine, Arch, 

 de physiol. norm, etpath., Paris, 1888, tome i., and others. 



"Schiifer, "Proc. Physiol. Soc.," Journ. Physiol., Cambridge and London, 1899, vol. 

 xxiv. p, xxxii. 



7 The existence of ascending fibres here was first noted by C. Bastian, Med-CMr. Trans., 

 London, 1867 (with figure). In 1879, Gowers called general attention to the degeneration 



