526 THE NERVOUS SYSTEM. 



from a nucleus in the medulla below that of the pneumogastric, 

 and the other from the intermediolateral tract of the cord. 

 The former is the accessory, and the latter the spinal, portion. 

 The accessory portion joins the pneumogastric, and is distributed 

 through the pharyngeal and superior laryngeal branches of that 

 nerve. It is also probable that the fibers of the pharyngeal 

 branch going to the muscles of the soft palate are fibers of this 

 portion of the spinal accessory. 



The inferior laryngeal nerve also contains fibers from this 

 nerve, probably from the internal, anastomotic, or accessory por- 

 tion, and experiments demonstrate that the power which the larynx 

 possesses to produce vocal sounds is due to these fibers, for when 

 the spinal accessory is torn out this power is lost. The other move- 

 ments of the larynx, those which take place during respiration, 

 are not interfered with under these circumstances, but only those 

 of phonation. The inferior laryngeal nerve is, then, only par- 

 tially made up of spinal accessory fibers : these fibers preside over 

 phonation. The other fibers, which are probably derived from the 

 facial, hypoglossal, or cervical, or all of them, provide the nervous 

 influence for the other movements. If the entire nerve is divided, 

 the laryngeal movements of both phonation and respiration will cease. 



The spinal or external portion is distributed to the trapezius 

 and sternomastoid muscles; it is therefore sometimes called the 

 " muscular branch." This branch is believed to be brought into 

 requisition when these muscles are needed for more than their 

 ordinary activity, for the nervous force to supply the latter is fur- 

 nished by cervical nerves. In unusual straining or in lifting, or 

 in the production of prolonged cries, these muscles are brought 

 into action, and to supply the additional innervation which these 

 acts seem to require is believed to be the office of the muscular 

 branch of the eleventh nerve. The spinal accessory is, then, 

 a motor nerve, although some writers regard a portion of the 

 fibers of the accessory part as being sensory. 



Hypoglossal. The apparent origin of this nerve is by filaments, 

 from 10 to 15 in number, from the groove between the pyramidal 

 and olivary bodies : its real origin is in a nucleus in the floor of 

 the fourth ventricle. It sends branches of communication to the 

 pneumogastric, the sympathetic, the first and second cervical, and 

 the gustatory. It is distributed to the sternohyoid, sternothyroid, 

 omohyoid, thyrohyoid, styloglossus, hyoglossus, geniohyoid, and 

 geniohyoglossus muscles. It is a motor nerve to the tongue, so 

 much so that it has been called the " motor linguae." The move- 

 ments over which it presides are those concerned in mastication 

 and deglutition and in the production of articulate speech. When 

 this nerve is paralyzed on one side, the tongue, when protruded, 

 is directed toward the paralyzed side. When both nerves are 

 involved in the paralysis all motion of the tongue ceases. 



