514 NERVOUS SYSTEM 



Following the nerve from its most inferior filament of origin upward, 

 it gradually increases in size by union with its other roots, enters the 

 cranial cavity by the foramen magnum, and passes to the jugular foramen, 

 by which it emerges, with the glosso-pharyngeal, the pneumogastric and 

 the internal jugular vein. 



In its course the spinal accessory anastomoses with several nerves. 

 Just as it enters the cranial cavity, it receives filaments of communica- 

 tion from the posterior roots of the upper two cervical nerves. These 

 filaments, however, are not constant. It frequently, though not con- 

 stantly, sends a few filaments to the superior ganglion, or the 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 receives a few filaments of communication. 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 

 internal, or anastomotic branch passes to the pneumogastric just below 

 the plexiform enlargement, which is sometimes called the ganglion of 

 the trunk of the pneumogastric. This branch is composed principally 

 if not entirely of the filaments that take their origin from the bulb. 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 the muscles of the 

 larynx except the crico-thyroid. The passage of the filaments from the 

 spinal accessory to the pharyngeal branch of the pneumogastric is 

 readily observed ; but the fact that filaments from this nerve pass to the 

 larynx by the recurrent laryngeal has been ascertained only by physio- 

 logical experiments. In the chimpanzee, however, the internal branch 

 does not go to the pneumogastric but passes directly to the muscles of 

 the larynx (Vrolik). 



The external, or large branch of the spinal accessory, called the mus- 

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

 upper third of the sterno-cleido-mastoid muscle. It then goes to the 

 anterior surface of the trapezius, which muscle receives its ultimate 

 branches of distribution. In its passage through the sterno-cleido-mas- 

 toid, 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 filaments 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. 



