FUNCTIONS OF THE SPINAL CORD AS A CONDUCTOR. 677 



conductors of the cord ; so that the stimulus of volition generated in one lateral half of 

 the brain always passes to the opposite half of the body. If a lesion occur in the brain 

 upon one side, so as to produce total paralysis of motion, the opposite side of the body is 

 paralyzed, while voluntary motion is absolutely intact on the side corresponding to the 

 injury. In the anterior pyramids of the medulla oblongata, the decussation of the fibres 

 is easily demonstrated anatomically. In view of these facts, concerning which there is 

 no difference of opinion, it only remains to show by physiological experiments that decus- 

 sation actually takes place at the medulla oblongata, and to submit to the same method 

 of inquiry the following important question : Assuming that crossing of motor fibres takes 

 place at the medulla, is this the sole seat of decussation of these fibres, or does it also 

 take place 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 action 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 con- 

 clusions drawn from anatomy and pathology are fully sustained. If the medulla be 

 exposed in a living animal, and "if a section is made longitudinally 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." (Brown-Sequard.) 



The question of decussation of motor fibres in the cord itself is one which can be 

 settled only by physiological experiments, as the course of the decussating fibres, if they 

 exist, cannot be demonstrated anatomically. It is remarkable that Galen submitted this 

 point to experimental investigation, 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, showing that the motor fibres do not cross the median line, at 

 least in this portion of the cord. Recent experiments upon the cervical portions of the 

 cord show that there is a very slight decussation of motor fibres in this situation. The 

 first observations pointing to this conclusion are those of Brown-Sequard. "There is 

 always, even in mammals, after a transversal section of the whole or a lateral half of the 

 spinal cord, at least some appearance of voluntary movements in the side of the injury, 

 and always also a diminution of voluntary movements in the opposite side; so that, in 

 animals, there seems to be in the spinal cord a decussation of a few of the voluntary 

 motor conductors. As there seems to be no such decussation in man, at least according 

 to several pathological facts, we shall not insist upon its existence in animals." 



Van Kempen has repeated and extended the very remarkable experiment of Galen, 

 with the most satisfactory results. This observer made a median, longitudinal section 

 of the cord in dogs and rabbits, at the site of the fifth, sixth, and seventh cervical ver- 

 tebra. " This experiment was followed by partial paralysis of voluntary movements in 

 the posterior extremities, so that the animal thus operated upon moved the posterior 

 limbs and was able to change his position, without, however, being able to raise 

 himself." 



As there is some difference in the results of observations upon different animals, and 

 as decussating motor fibres have never been demonstrated in man, it is impossible to 

 apply the above experiments without reserve to the human subject ; but they show, 

 nevertheless, that, in mammals, the motor columns of the cord probably do not decussate 

 in the dorso-lumbar region; that partial decussation occurs in the cervical ivgion ; and 

 that the decussation is completed in the anterior pyramids of the medulla oblongata. 



Transmission of Sensory Impressions in the Cord. Early in the physiological his- 

 tory of this portion of the nervous system, Longet made a number of experiments, which 



