SPINAL ACCESSORY NERVE. 559 



thyroid. The passage of the filaments from the spinal accessory to the pharyn- 

 geal branch of the pneumogastric is easily observed ; but the fact that fila- 

 ments from this nerve pass to the larynx by the recurrent laryngeal has been 

 ascertained by physiological experiments. 



The external, or large branch of the spinal accessory, called the muscular 

 branch, penetrates and passes through the posterior portion of the upper 

 third of the sterno-cleido-mastoid muscle, and goes to the anterior surface of 

 the trapezius, which muscle receives its ultimate branches of distribution. 

 In its passage through the sterno-cleido-mastoid, it joins with branches from 

 the second and third cervical nerves and sends filaments of distribution to 

 the muscle. Although the two muscles just mentioned receive motor fila- 

 ments from the spinal accessory, they are also supplied from the cervical 

 nerves; and consequently they are not entirely paralyzed when the spinal 

 accessory is divided. 



Properties and Uses of the Spinal Accessory. Notwithstanding the great 

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

 it has been demonstrated that their stimulation produces convulsive move- 

 ments in certain muscles. By stimulating the filaments that arise from the 

 medulla oblongata, contractions of the muscles of the pharynx and larynx 

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

 ulation of the roots arising from the spinal cord produces movements of the 

 two muscles just mentioned and absolutely no movements in the larynx (Ber- 

 nard). 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 distributed to the muscles of the 

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

 no-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 be divided, 

 the peripheral extremity manifests recurrent sensibility, but the central end 

 is also sensible, probably from direct filaments of communication from the 

 cervical nerves and the pneumogastric. 



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

 gastric. Bischoff attempted to ascertain the uses 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 sec- 

 tion of the nerves, that no satisfactory results were obtained. In two suc- 

 ceeding 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 



