MOTOE COXDUCTIOJr IN" THE SPINAL CORD. 283 



the decnssation of the fibres is easily demonstrated ana- 

 tomically. In view of these facts, concerning which there 

 is no difference of opinion, it only remains to show by 

 physiological experiments that decussation actually takes 

 place at the medulla oblongata, and to submit to the same 

 method of inquiry the following important question : Assum- 

 ing that crossing of motor fibres takes place at the medulla, 

 is this the sole seat of decussation of these fibres, or does it 

 also exist in certain portions of the cord below ? 



The question of decussation at the medulla oblongata is 

 easily answered. In the first place, we have the crossed ac- 

 tion in hemiplegia and the easy anatomical demonstration 

 of the decussating fibres. The experimental confirmation 

 of these facts is not so simple, for the reason that animals 

 survive operations upon the medulla oblongata for a very 

 short time. As far as can be learned, however, from the 

 latter mode of inquiry, the conclusions drawn from anatomy 

 and pathology are fully sustained. If the medulla be ex- 

 posed in a living animal, and " if a section is made longitu- 

 dinally just at the place of the decussation of the anterior 

 pyramids, so as to divide completely all of the decussating 

 elements, we find that, although the animal lives some time 

 after the operation, it has no voluntary movement at all in 

 any of the limbs, which are almost always the seat of con- 

 vulsions." l 



The question of decussation of motor fibres in the cord 

 itself is one which can be settled only by physiological ex- 

 periments, as the course of the decussating fibres, if they 

 exist, cannot be demonstrated anatomically. It is remark- 

 able that Galen submitted this point to experimental inves- 

 tigation, by dividing the cord longitudinally in the median 

 line in the lumbar region. This operation was not followed 

 by loss of voluntary power in the lower extremities, show- 

 ing that the motor fibres do not cross the median line, at 



1 BROWN-SEQUARD, Physiology and Pathology of the Central Nervous System, 

 Philadelphia, 1860, p. 49. 



