MEDIATE SPINAL SYSTEMS. 809 



Lenhossek, however, denies that the ventral pyramidal tract crosses ; he con- 

 siders it passes to the homonymous ventral horn. 



Though the main bulk of the pyramidal system is crossed, it is in part 

 uncrossed. Hence degeneration in both lateral columns follows unilateral 

 lesions of cortex cerebri. 1 The relative amount of the uncrossed and crossed 

 degenerations varies much according as different regions of the motor cortex are 

 the site of lesion. A minority of the pyramidal fibres, when arrived at the 

 caudal end of the bulb, instead of sloping across the median sagittal plane, 

 deviate 2 to the homonymous lateral column, and lie there in a position symmet- 

 rical with the crossed area occupied by the main crossed division of the system. 

 This uncrossed pyramidal system extends also the whole length of the cord. 



The fibres of the pyramidal system are the latest in the cord to become 

 myelinated ; 3 and the slowest, after section in the cord, to show degenerative 

 alteration. 4 The pyramidal system, so far as is known, exists only in mammals. 5 

 There is no other system which shows such increase in relative size as traced 

 from lower to higher mammalian types. Hardly perceptible as a spinal 

 tract in the rabbit, it in the monkey is much larger than in other laboratory 

 forms, and in man is larger still. This relative increase is shown not merely 

 by the tract occupying a larger proportion of the transverse area of the cord, but 

 by its fibres being relatively more densely set within that area. Hence the 

 " scar " left by degeneration of a pyramidal tract is in man not only relatively 

 somewhat larger than in that of the dog, but far fewer sound nerve fibres 

 remain in the sclerosed area. 



In its spinal course the pyramidal system lies in the lateral column, 

 nowhere actually abutting on the ventral grey cornu. The existence of a 

 direct synapsis between the pyramidal axon and the ventral cornual root cell 

 has been generally assumed, though rejected by some, and never definitely 

 proven. 6 After section of the tract, the degeneration of fine medullate fibres 

 in the ventral cornu has been both asserted 7 and denied. 8 The collaterals 



1 Pitres, Bull. Soc. de physiol. de Bordeaux, 1880, tome i. p. 97 ; Gaz. hebd. de m&t., 

 Paris, 1881, p. 429 ; Progres med., Paris, 1882, p. 528 ; Arch, de physiol. norm, et path., 

 Paris, 1884, tome iii. p. 142 ; Moeli, Arch. f. Psychiat., Berlin, 1883 ; Schafer (Ferrier and 

 Yeo's monkey), Journ. Physiol., Cambridge and London, 1883, vol. iv. ; Sherrington, 

 ibid., 1885, vol. vi., 1889, vol. x. ; Lowenthal, "Diss.," Geneve, 1885 ; Bianchi e Abundo, 

 Psichiatria, Napoli, 1886; March! and Algeri, Riv. sper. difreniat., Reggio-Emilia, 1887, 

 tomo xii. p. 3 ; Unverricht, Neurol. Centralbl., Leipzig, 1890, Bd. ix. S. 483 ; Sandmeyer, 

 Ztschr. f. Biol., Mtinchen, 1891, Bd. xxviii. S. 177 ; Singer and Miinzer, Denkschr. d. 

 k. Akad. d. Wissensch., Wien, 1890. 



a W. Muratoff, Arch. f. Physiol., Leipzig, 1893 ; Sherrington, Lancet, London, Feb. 3, 

 1894 ; Neurol. Centralbl., Leipzig, 1894, Bd. xiii. S. 341; Mellus, Proc. Roy. Soc. London, 

 1894, vol. Iv. p. 208 ; Boyce, Phil. Trans., London, 1895 ; Dejerine and Thomas, Arch. 

 de physiol. norm, et path., Paris, April 1896 ; Rothmann, Neurol. Centralbl., Leipzig, June 



1896, and others. 3 Flechsig and others. 



4 Schaffer, Neurol. Centralbl., Leipzig, 1895, Bd. ix. S. 386, found first sign of degeneration 

 by the Marchi method on the fourteenth day in the cat ; see also Worotinsky, ibid.,~Dec. 1897. 

 On the ninth day in the cat I have found no sign of their degeneration by that method, but 

 have on the twelfth day, and with carmine stain I got distinct evidence in the dog on the 

 ninth day, Jo-urn. Physiol., Cambridge and London, 1885, vol. vi. ; and Homen with acid- 

 fuchsin in the dog on the fifth day, Fortschr. d. Med., Berlin, 1885, S. 267. All observers 

 are agreed that this onset is more tardy than that of degeneration in some other spinal 

 fibres, especially those of GolPs column, where it is obvious in three to four days after spinal 

 transection. Langley and Anderson suggest that small fibres are the earliest to show 

 degeneration, "Proc. Physiol. Soc.," May 1894, Journ. Physiol., Cambridge and London, 

 vol. xvi. p. 12. 



5 In the guinea-pig the pyramidal tract runs in the dorsal column of the cord. 



6 v. Lenhossek, "Der feinere-Bau des Nerven systems," Aufl. 2, Leipzig, 1895; Monakow 

 (Arch. f. Psychiat., Berlin, 1895, Bd. xxvii.) argue the intervention of a relay cell of the Golgi 

 type, 2. 



7 Sherrington, Journ. Physiol., Cambridge and London, 1890, vol. xi. p. 399 (Weigert's 

 method) ; Mingazzini, Riv. sper. difreniat., Reggio-Emilia, 1892, tomo xviii. 



8 Starlinger, Jahrb. f. Psychiat., 1896, Bd. xv. ; Redlich, Neurol. Centralbl., Leipzig, 



1897, Bd. xvi. S. 824; Schafer, "Proc. Physiol. Soc.," Journ. Physiol., Cambridge and 

 London, 1899, vol. xxiv. 



