SPINAL AOCESSOKY NERVE. 627 



food between the teeth by pressure with the hand. In the rare instances in which both 

 facial nerves are paralyzed, there is very great difficulty in mastication, from the cause 

 just mentioned. 



The functions of the external branches of the facial are thus sufficiently simple ; and 

 it is only as its deep branches affect the taste, the movements of deglutition, etc., that it 

 is difficult to ascertain their exact office. As this is the nerve of expression of the face, 

 it is in the human subject that the phenomena attending its paralysis are most prominent. 

 When both sides are affected, the appearance is most remarkable, the face being abso- 

 lutely expressionless and looking as if it had been covered with a mask. 



/Spinal Accessory and Sublingual JVerves. 



A description of the properties and functions of the spinal accessory and the sublin- 

 gual completes the physiological history of the motor nerves emerging from the cranial 

 cavity. The functions of these nerves are important, and, in the case of the spinal 

 accessory, they possess considerable interest, from the fact that physiological investigations 

 have, only within a few years, determined the significance of certain of its anatomical 

 relations. As we have done in studying the other motor nerves, we shall treat succes- 

 sively of their anatomical relations, general properties and functions. 



Spinal Accessory JSTerve. (Third Division of the Eighth Nerve.) 



The spinal accessory nerve, from the remarkable extent of its origin, its important 

 anastomoses with other nerves, and its curious course and distribution, has long engaged 

 the attention of anatomists and physiologists, who have advanced many theories with 

 regard to its office. We shall content ourselves, however, with a simple description of 

 its anatomy as it appears from late researches, and shall begin its physiological history 

 with comparatively recent experiments, which alone have advanced our positive knowl- 

 edge of its properties. 



Physiological Anatomy of the Spinal Accessory . The origin of this nerve is very exten- 

 sive. A certain portion arises from the lower half of the medulla oblongata, and the rest 

 takes its origin below, from the upper two-thirds of the cervical portion of the spinal 

 cord. That portion of the root which arises from the medulla oblongata is called, by 

 the French, the bulbar portion, the roots from the cord constituting the spinal portion. 

 Inasmuch as there is a marked difference between the functions of these two portions, 

 the anatomical distinction just mentioned is important. 



The superior roots arise by four or five filaments from the lower half of the medulla 

 oblongata, below the origin of the pneumogastrics. These filaments of origin, in prepara- 

 tions hardened by prolonged immersion in alcohol, are shown to be connected with the 

 lateral portion of the medulla, and not with the posterior columns. Their origin seems, 

 therefore, to be from the motor tract. 



The spinal portion of the nerve arises from the upper part of the cervical division 

 of the spinal cord, between the anterior and posterior roots of the upper four or five 

 cervical nerves. The filaments of origin are from six to eight in number. The most 

 inferior of these is generally single, the other filaments being frequently arranged in 

 pairs. These take their origin from the lateral portion of the cord, rather nearer the 

 posterior median line than the roots from the medulla oblongata. 



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, in connection 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 communication from the posterior roots of the 



