SPINAL ACCESSORY NERVE 515 



Properties and Uses of the Spinal Accessory. Notwithstanding the 

 difficulty in exposing and operating on the roots of the spinal accessory, 

 it has been demonstrated that their stimulation produces convulsive 

 movements in certain muscles. By stimulating the filaments that arise 

 from the bulb, contractions of the muscles of the pharynx and larynx 

 are produced, but no movements of the sterno-mastoid and trapezius. 

 Stimulation of the roots arising from the spinal cord produces move- 

 ments of the two muscles just mentioned and no movements in the 

 larynx. In view of these experiments, it is evident that the true fila- 

 ments of origin of the spinal accessory are motor ; and it is further evi- 

 dent that the filaments from the bulb are distributed to the muscles of 

 the pharynx and larynx, while the filaments from the spinal cord go to 

 the sterno-cleido-mastoid and trapezius. 



The trunk of the spinal accessory, after the nerve has passed out of 

 the cranial cavity, has a certain degree of sensibility. If the nerve is 

 divided, the peripheral extremity manifests recurrent sensibility, but the 

 central end also is sensible, probably from direct filaments of communi- 

 cation from the cervical nerves and the pneumogastric. 



Uses of the Internal Branch from the Spinal Accessory to the Pneumo- 

 gastric. Bischoff (1832) attempted to ascertain the uses of this branch 

 by dividing the roots of the spinal accessory on both sides in a living 

 animal. The results of his experiments may be stated in a very few 

 words : He attempted to divide all the roots of the nerves on both 

 sides by dissecting down to the occipito-atloid space and penetrating 

 into the cavity of the spinal canal. In the first three experiments on 

 dogs, the animals died so soon after section of the nerves that no satis- 

 factory results were obtained. In two succeeding experiments on dogs, 

 the animals recovered. After division of the nerves the voice became 

 hoarse, but a few weeks later it became normal. On killing the ani- 

 mals, an examination of the parts showed that some of the filaments of 

 origin had not been divided. An experiment was then made on a goat, 

 but this was unsatisfactory, as the roots were not completely divided. 

 Finally another experiment was made on a goat. In this the results 

 were more satisfactory. After division of the nerve on one side, the 

 voice became hoarse. As the filaments were divided on the opposite 

 side, the voice was enfeebled, until finally it became extinct. The sound 

 emitted afterward was one that could in no wise be called voice (" qui 

 neutiquam vox appellari potuit"}. 



Bernard, who determined exactly the influence of the spinal acces- 

 sory over the vocal movements of the larynx, first repeated the experi- 

 ments of Bischoff ; but the animals operated on died so soon from 

 hemorrhage or other causes that his observations were not satisfactory. 



