556 THE CEAXIAL NERVES 



and a third to the ganglion of the root of the pnemno-gastric nerve. The last is 

 not constant. 



There is sometimes likewise a filament from the digastric branch of the facial 

 nerve, which, piercing the digastric muscle, joins the glosso-pharyngeal nerve be- 

 low the petrous ganglion. 



The ti/iiqmnk: branch (nerve of Jacobson) arises from the petrous ganglion, and 

 is conducted to the tympanum by a special canal, the orifice of wfiich is in the 

 ridge of bone between the jugular fossa and the carotid foramen. On the inner 

 wall of the tympanum the nerve joins with a twig from the sympathetic forming a 

 plexus (tj'mpanic), and distributes filaments to the membrane lining the tym- 

 panum and the Eustachian tube, as well as one to the fenestra rotunda,, and 

 another to the fenestra ovalis. 



From the tympanic nerve are given three connecting hrancJies. by which it 

 communicates with other nerves ; and which occupy channels given off from the 

 osseous canal through which the nerve enters the tympanum. One branch enters 

 the carotid canal and joins with the sympathetic on the carotid artery. A second 

 is united to the large superficial petrosal nerve, as this lies in the hiatus Fallopii. 

 And the third is directed upwards, beneath the canal for the tensor tympani 

 muscle, towards the surface of the petrous portion of the temporal bone, where 

 it becomes the i<i)tnll jxtroml ncvcc ; and under this name it is continued to the 

 exterior of the skull through a small aperture in the sphenoid and temporal 

 bones, to end in the otic ganglion. As this petrosal nerve passes the ganglifonn 

 enlargement of the facial, it has a connecting filament with that enlargement, 

 which is by some considered its j^rincipal posterior termination. 



Jacobson described an interior or internal branch from the tj-mpanic nerve to 

 the spheno-palatine ganglion. 



Branches distributed, in the neck. — The carotid hranchcfi course along the 

 internal carotid artery, and unite with the pharyngeal branch of the pneumo- 

 gastric, and with branches of the sympathetic nerve. 



The j)hari/nf/t'(il Iranckcs, three 01' four in number, unite opposite the middle 

 constrictor of the pharjTix with branches of the pneumo-gastric and sj'nipathetic 

 to form the j)hftri/nf/ral jjlc.ru.'^. Nerves to the mucous membrane of the pharynx 

 perforate the muscles, and extend upwards to the base of the tongue and the 

 epiglottis, and downwards nearly to the hyoid bone. 



The mu.scular branches are given to the stj-lo-pharjTigeus and constrictor 

 muscles. 



Tunsilitic branches. — "WTien the glosso-pharjnigeal nerve is near the tonsil, some 

 branches are distributed on that body in a kind of plexus (circulus tonsillaris). 

 From these nerve offsets are sent to the soft palate and the isthmus of the fauces. 



Lingual branches. — The glosso-phar^aigeal nerve divides into two parts at the 

 border of the tongue. One turns to the upper surface of the tongue, supplying 

 the mucous membrane at its base : the other perforates the muscular structure, 

 and ends in the mucotis membrane on the lateral part of the tongue. fSome fila- 

 ments enter the circumvallate papillae. 



Variety. — In one case a branch from the glosso-pharyngeal supplied the 

 mylo-hyoid muscle and the anterior belly of the digastric, the normal mylo- 

 hyoid nerve being wanting. (Guy"s Hosp. Reports, vol. xiv.. p. 4;!G.) 



SmniARY. — The frlosso-pharyngeal nerve distributes branches to the 

 mucous memliraue of the ton^ijue, pharynx, tympanum, and Eustachian 

 tube. The muscles supplied by it are some of those of the pharynx and 

 base of the tongue. It is connected with the following nerves, viz., tlie 

 lower maxillary division of the fifth, the facial, the pneumo-gastric (the 

 trunk and branches of this nerve), and the sympathetic. 



II.— PNEUMO-GASTRIC NERVE. 



The pneumo-gastric nerve (nervus vagus, parvagum) has the longest 

 course <.»f any of the cranial nerves. It extends through the neck and 

 the cavity of the chest to the upper part of the abdomen ; and ib 



