CHAP. XI.] FUNCTIONS OF THE SPINAL CORD. 307 



side, and the posterior roots on the other, voluntary power without 

 sensation will remain in the latter, and sensation without voluntary 

 power in the former. 



Valentin, Seubert, Panizza, and Longet have performed similar 

 experiments upon mammiferous animals with precisely the same 

 effects. 



The conclusion to be derived from these experiments is as fol- 

 lows : that the anterior root of each spinal nerve is motor, and the 

 posterior sensitive. 



Comparative anatomy confirms this conclusion, by shewing that 

 a similar arrangement of the spinal roots prevails among all classes 

 of vertebrate animals, and that, if in any particular class of animals 

 either the motor or sensitive power predominate, there is in cor- 

 respondence with it a marked development of the anterior or pos- 

 terior roots ; and the frequent occurrence of paralysis of sensation 

 and motion, as a consequence of disease within the spinal canal, 

 also tends to the same inference. 



Magendie affirms that the anterior root is slightly sensitive, 

 owing, as Kronenburg has shewn, to an anastomotic filament 

 which it derives from the posterior root. 



Functions of the Spinal Cord. Since nerves of sensation and mo- 

 tion have their origin from the cord, it cannot be doubted that this 

 organ is the medium for the reception and propagation, first, of 

 sensitive impressions made upon those surfaces on which its nerves 

 are distributed, and secondly, of those impulses which are the 

 ordinary excitants of muscular movements. 



Experiments and clinical observation, however, shew that sensa- 

 tion and voluntary motion are not connected with, or dependent on, 

 the spinal cord alone. If the connexion of this organ with the 

 encephalon be perfect, and uninterrupted by any solution of con- 

 tinuity, morbid deposit in it, or morbid growth causing compression, 

 then the essential condition for the full play of the nervous force, 

 whether for sensation or voluntary motion, is fulfilled. But if the 

 cord be severed just below the plane of the occipital foramen as when 

 an animal is pithed, all voluntary power over the parts supplied by 

 spinal nerves ceases, and all sensation in those parts disappears at 

 the same time. Here the cord itself is uninjured; but its con- 

 tinuity with the encephalon is destroyed. 



In cases of injury to the vertebral column, causing fracture and 

 displacement of the vertebrae, and destruction of the cord, the parts 

 supplied from that portion of the cord which is below the seat of 

 injury arc paralysed as regards voluntary motion and sensation. 



x 2 



