SPINAL ACCESSORY NERVE. 629 



cles of the pharynx and larynx and no movements of the sterno-mastoid and trapezius. 

 Galvanization of the roots arising from the spinal cord produced movements of the two 

 muscles just mentioned and absolutely no movements in the larynx. In view of these 

 experiments, it is evident that the true filaments of origin of the spinal accessory are 

 motor ; and it is farther evident that the filaments from the medulla oblongata are dis- 

 tributed 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, 

 is endowed with a certain degree of sensibility. If the nerve be divided, the peripheral 

 extremity manifests recurrent sensibility, but the central end is also sensible, proba- 

 bly from direct filaments of communication from the cervical nerves and the pneumo- 

 gastric. As we have remarked, however, in treating of the properties of some other of 

 the cranial nerves, it is exceedingly difficult to note satisfactorily a slight degree of sensi- 

 bility in nerves that can be exposed only by a tedious and painful operation. 



The functions of the external, or muscular branch of the spinal accessory are suffi- 

 ciently evident ; and the effects of the destruction of the nerves on both sides, as far as 

 this branch is concerned, simply resolve themselves into the phenomena due to partial 

 paralysis of the sterno-mastoid and trapezius ; but the functions of the branch which 

 joins the pneumogastric are much more complex. 



Functions of the Internal Branch from the Spinal Accessory to the Pneumogastric. 

 Bischoff attempted to ascertain the functions of this branch by dividing the roots of the 

 spinal accessory upon both sides in a living animal. The results of his experiments may be 

 stated in a very few words : He attempted to divide all of the roots of the nerves upon 

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

 of the spinal canal. In the first three experiments upon dogs, the animals died so soon 

 after section of the nerves, that no satisfactory results were obtained. In two succeed- 

 ing experiments upon dogs, the animals recovered. After division of the nerves, the voice 

 became hoarse, but a few weeks later, it became normal. On killing the animals, an 

 examination of the parts showed that some of the filaments of origin had not been 

 divided. An experiment was then made upon a goat, but this was unsatisfactory, as the 

 roots were not completely divided. Finally, another experiment was made upon a goat. 

 In this the results were more satisfactory. After division of the nerve upon one side, 

 the voice became hoarse. As the filaments were divided upon the opposite side, the 

 voice was enfeebled, until finally it became extinct. The sound emitted afterward was 

 one which could in nowise be called voice (" qui neutiquam vox appellari potuit "). This 

 experiment was made in the presence of Tiedemann and Seubertus and was not re- 

 peated. 



Bernard, whose ingenious experiments determined exactly the influence of the spinal 

 accessory over the vocal movements of the larynx, first repeated the experiments of Bis- 

 choff; but the animals operated upon died so soon, from haemorrhage or other causes, 

 that his observations were not satisfactory. After many unsuccessful trials, he succeeded 

 in overcoming all difficulties, by following the trunk of the nerve back to the jugular 

 foramen, seizing it here with a strong pair of forceps, and drawing it out by the roots. 

 This operation is difficult, but we have several times performed it with entire success, 

 and have verified, in every regard,- the facts observed by Bernard. Within the last year, 

 the excellent assistant to the chair of Physiology at the Bellevue Hospital Medical Col- 

 lege, Dr. 0. F. Roberts, has succeeded in extirpating these nerves for class-demon- 

 strations. The operation is generally most successful in cats, although Bernard has 

 succeeded frequently in other animals. 



The operative procedure employed by Bernard is the following : The trunk of the 

 nerve is exposed as it passes through the sterno-cleido-mastoid muscle. It is then fol- 

 lowed up by careful dissection, avoiding blood-vessels as much as possible, to the poste- 

 rior foramen lacerum. when the sublingual is seen crossing the course of the pneumo- 



