168 NERVOUS SYSTEM. 



emerges, in connection with the glosso-phar yngeal, the pneu- 

 mogastric, and the internal jugular vein. 



In its course, the spinal accessory anastomoses with sev- 

 eral nerves. Just as it enters the cranial cavity, it receives 

 filaments of communication from the posterior roots of the 

 upper two cervical nerves. These filaments, however, are 

 not constant. It frequently, though not constantly, sends a 

 few filaments to the superior ganglion, or ganglion of the 

 root of the pneumogastric. After it has emerged by the 

 jugular foramen, it sends a branch of considerable size to 

 the pneumogastric, from which nerve it also receives a few 

 filaments of communication. This branch will be again re- 

 ferred to in connection with the distribution of the nerve. 

 In its course, it also receives filaments of communication 

 from the anterior branches of the second, third, and fourth 

 cervical nerves. 



In its distribution, the spinal accessory presents two 

 branches. The first, or anastomotic branch, passes to the 

 pneumogastric just below the plexiform enlargement which 

 is sometimes called the ganglion of the trunk of the pneu- 

 mogastric. 



The internal, or anastomotic branch, is composed princi- 

 pally, if not entirely, of the filaments that take their origin 

 from the medulla oblongata. As it joins the pneumogastric, 

 it subdivides into two smaller branches. The first of these 

 forms a portion of the pharyngeal branch of the pneumo- 

 gastric. The second becomes intimately united with the 

 pneumogastric, lying at its posterior portion, and furnishes 

 filaments to the inferior, or recurrent laryngeal branch, 

 which is distributed to all of the muscles of the larynx ex- 

 cept the crico-thyroid. The passage of the filaments 'from 

 the spinal accessory to the pharyngeal branch of the pneu- 

 mogastric is easily observed ; but the fact that filaments 

 from this nerve pass to the larynx by the recurrent laryn- 

 geal has been ascertained only by physiological experiments. 



The external, or large branch of the spinal accessory, 



