SPINAL ACCESSORY. 627 



enters a small bony canal at the base of the petrous portion of the temporal 

 bone ; the lower opening of which is situated on the bony ridge which sepa- 

 rates the carotid canal from the jugular fossa. Jacobson's nerve ascends to the 

 tympanum, enters that cavity by an aperture in its floor close to the inner wall, 

 and divides into three branches, which are contained in grooves upon the sur- 

 face of the promontory. 



Its branches of distribution are, one to the fenestra rotunda, one to the fenestra 

 ovalis, and one to the lining membrane of the Eustachian tube and tympanum. 



Its branches of communication are three, and occupy separate grooves on the 

 surface of the promontory. One of these arches forwards and downwards to 

 the carotid canal to join the carotid plexus. A second runs vertically upwards 

 to join the greater superficial petrosal nerve, as it lies in the hiatus Fallopii. 

 The third branch, the lesser petrosal, runs upwards and forwards towards the 

 anterior surface of the petrous bone, and passes through a small aperture in 

 the sphenoid and temporal bones, to the exterior of the skull, where it joins the 

 otic ganglion. This nerve, in its course through the temporal bone, passes by 

 the ganglionic enlargement of the facial, and has a connecting filament with it. 



The branches of the glosso-pharyngeal nerve are the carotid, pharyngeal, 

 muscular, tonsillar, and lingual. 



The carotid branches descend along the trunk of the internal carotid artery as 

 far as its point of bifurcation, communicating with the pharyngeal branch of 

 the pneumogastric, and with branches of the sympathetic. 



The pharyngeal branches are three or four filaments which unite opposite the 

 Middle Constrictor of the pharynx with the pharyngeal branches of the pneu- 

 mogastric, superior laryngeal, and sympathetic nerves, to form the pharyngeal 

 plexus, branches from which perforate the muscular coat of the pharynx to 

 supply the mucous membrane. 



The muscular branches are distributed to the Stylo-pharyngeus. 



The tonsillar branches supply the tonsil, forming a plexus (circulus tonsil- 

 laris) around this body, from which branches are distributed to the soft palate 

 and fauces, where they anastomose with the palatine nerves. 



The lingual branches are two in number ; one supplies the mucous membrane 

 covering the surface of the "base of the tongue, the other perforates its substance, 

 and supplies the mucous membrane and papillas of the side of the organ. 



The Spinal Accessory Nerve consists of two parts ; one, the accessory part to 

 the vagus, and the other the spinal portion. 



The accessory part, the smaller of the two, arises by four or five delicate fila- 

 ments from the lateral tract of the cord below the roots of the vagus ; these 

 filaments may be traced to a nucleus of gray matter at the back of the medulla, 

 below the origin of the vagus. It joins, in the jugular foramen, with the upper 

 ganglion of the vagus by one or two filaments, and is continued into the vagus 

 below the second ganglion. It gives branches to the pharyngeal and superior 

 laryngeal branches of the vagus. 



The spinal portion, firm in texture, arises by several filaments from the lateral 

 tract of the cord, as low down as the sixth cervical nerve ; the fibres pierce the 

 tract, and are connected with the anterior horn of the gray matter of the cord. 

 This portion of the nerve ascends between the ligamentum denticulatum and 

 the posterior roots of the spinal nerves, enters the skull through the foramen 

 magnum, and is then directed outwards to the jugular foramen, through which 

 it passes, lying in the same sheath as the pneumogastric, separated from it by 

 a fold of the arachnoid, and is here connected with the accessory portion. At 

 its exit from the jugular foramen, it passes backwards behind the internal jugu- 

 lar vein, and descends obliquely behind the Digastric and Stylo-hyoid muscles 

 to the upper part of the Sterno-mastoid. It pierces that muscle, and passes 

 obliquely across the suboccipital triangle, to terminate in the deep surface of 

 the Trapezius. This nerve gives several branches to the Sterno-mastoid during 

 its passage through it, and joins in its substance with branches from the third 



