v SPINAL COED AND NEEVES 343 



anomalous failure of the conducting paths to decussate, or by a 

 double decussation. Clinical cases have in fact been described in 

 which the one or the other had occurred. But these exceptions 

 are rare. 



Does this decussation occur in the brain, in the bulb, or in the 

 cord ? The interhemispherical commissure, the so-called corpus 

 callosum, contains simple paths of interhemispherical association, 

 and is not related to cerebro-spinal conducting paths. The 

 majority of the motor cerebro-spinal fibres which form the 

 pyramidal tracts cross in the bulb, while many of the fibres 

 which do not cross here (direct ventral and lateral pyramidal 

 bundles) decussate in the cord, passing from one side to the other 

 by the white and grey commissures. . In any case a partial spinal 

 decussation of the motor paths is established, both by histological 

 facts and by bilateral descending degeneration of the direct and 

 crossed pyramidal tracts after unilateral traumatic injury or 

 pathological lesions of the cord (W. Miiller, Charcot, Pitres, and 

 others). 



The decussation of the sensory paths is known to occur partly 

 in the so-called interolivary region of the bulb, above and dorsal 

 to the decussation of the motor pyramidal tracts ; but certain 

 collaterals of the medullated fibres of the dorsal roots also cross 

 through the anterior commissure. It may therefore be stated in 

 general terms that anatomical facts show that the long motor and 

 sensory conduction paths cross from one side to the other, to a 

 small extent in the cord, to a much larger extent in the brain-stem. 



The effects of unilateral section of the cord must now be con- 

 sidered in more detail. 



Few problems in the physiology of the nervous system have 

 been more discussed, and the results and interpretation differ 

 widely. 



Galen was the first who performed and attempted to follow up 

 the total or partial transection of the cord (probably on monkeys), 

 and it is astonishing to see how closely his results agree with the 

 most recent observations. 



Many workers took up this subject in the early half of the 

 nineteenth century, but after the first experiments of Fodera 

 (1823), Schops (1827), J. van Deen (1838), Valentin (1839), 

 Stilling (1842), Budge (1842), Eigenbrodt (1848), the only authors 

 who published repeated communications upon it were Brown- 

 Sequard in France and M. Schiff in Germany and Italy. 



Brown-Sequard's theory, which was accepted by most physio- 

 logists and quoted in nearly all text-books of the physiology and 

 pathology of the nervous system, may be summed up in the 

 following propositions : (a) Nearly all the motor fibres cross in the 

 medulla oblongata, very few in the cord ; (&) nearly all the sensory 

 paths cross in the cord, very few in the medulla oblongata. 



