360 



THE CRANIAL NERVES. 



branch of the pneumo-gastric ; and a third, which however is not constant, joins 

 the ganglion of the root of the pneumo-gastric nerve. 



The glosso-pharyngeal nerve is also joined below the petrosal ganglion, in many 

 cases, by a communicating branch from the facial nerve (p. 254). 



The tympanic branch (nerve of Jacobson) ascends from the petrosal ganglion, 

 in company with the tympanic branch of the ascending pharyngeal artery, through 

 a small canal, the orifice of which is seen on the ridge of bone between the jugular 

 fossa and the carotid foramen. Having gained the inner wall of the tympanum, the 

 nerve runs upwards and forwards in a groove on the surface of the promontory, and, 

 after giving (or receiving) several branches, leaves the cavity at its upper and fore 

 part, where it becomes the small superficial petrosal nerve. The latter traverses a 

 small canal, which crosses beneath the upper end of the canal of the tensor tympani 

 muscle, and emerges on the upper surface of the petrous portion of the temporal 

 bone, immediately external to the hiatus Fallopii. Then inclining downwards, the 



Fig. 177. THE TYMPANIC NERVE OF THE LEFT SIDE IN ITS CONNEC- 

 TION WITH THE FACIAL. (KraUSC.) f 



1, facial nerve, proximal end ; 2, geniculate ganglion ; 3, facial 

 nerve, distal end ; 4, nerve to fenestra ovalis ; 5, ganglion-cells in 

 tympanic nerve ; 6, nerve of fenestra rotunda ; 7, tympanic nerve from 

 glosso-pharyngeal ; 8, small deep petrosal nerve ; 9, nerve to Eustachian 

 tube ; 10, filament to geuiculate ganglion ; 11, small superficial petro- 

 sal nerve ; 12, petrosal branch of middle meningeal artery ; 13, large 

 superficial petrosal nerve ; 14, Pacinian corpuscles in the dura mater. 



nerve passes from the skull through the fissure between 

 the petrous and the great wing of the sphenoid, or 

 occasionally through a small aperture in the latter bone, 

 and terminates in the otic ganglion. As it lies in its 

 canal, the small superficial petrosal nerve is joined by a 

 filament of communication from the geniculate ganglion 

 of the facial nerve, or from the large superficial petrosal 

 nerve close to that ganglion. 



The branches of the tympanic nerve are partly dis- 

 tributed to the mucous lining of the middle ear, and 

 partly form communications with other nerves, giving 

 rise to what is called the tympanic plexus. Of the former 

 set, the principal branches are one directed forwards to the Eustachian tube, and 

 two backwards to the neighbourhood of the fenestra rotunda and fenestra ovalis, 

 and to the mastoid cells. The communicating branches are, in addition to the 

 small superficial petrosal nerve with its filament of union with the facial, one or two 

 twigs (carotico-tympanic) which pass downwards and forwards through the anterior 

 wall of the tympanum to the carotid canal and join the sympathetic on the carotid 

 artery, and the small deep petrosal nerve which runs forwards in a minute canal in 

 the substance of the processus cochleariformis and enters the foramen lacerum, 

 where it joins the carotid plexus of the sympathetic, or sometimes one of the large 

 petrosal nerves (figs. 165, 170). 



The tympanic nerve while in its canal is surrounded by a small fusiform mass of soft 

 vascular tissue which has been called the tympanic gland (Krause) ; and as it lies in the 

 tympanum it contains numerous nerve-cells in irregular groups. 



B. Branches distributed in the neck. 



Pharyngeal branches. The largest of these (carotid branch, pharyngeal 

 division of the glosso-pharyngeal nerve Henle) descends along the internal carotid 



