160 ANTHROPOLOGY. 



bony canals leading into the substance of the axis, and pass out between 

 the osseous plates forming the lamina spiralis. The nerve divides into 

 uiimerous branches which anastomose with each other, and spread out into 

 a delicate nervous membrane, or according to some, terminate in the form 

 of papillae. 



The facial or portio-d.ura nerve enters the meatus along with the auditory, 

 ;md entering the aqueduct of Fallopius, passes to the hiatus Fallopii, where 

 it is joined by the superior petrosal branch of the vidian and presents a 

 ganglion enlargement. The cJiordu tympani may be regarded either as the 

 t'ontinued petrosal branch of the vidian, or as proceeding from the last- 

 mentioned ganglion. It passes into the ear, winds among the tympanic 

 l)ones, and escapes bj»^ a bony canal in the glenoid fossa. The tympanic 

 ■niexus is a delicate network, chiefly formed by the tympanic branch of the 

 ;,;losso-pharyngeal nerve, or the nerve of Jacobson. 



Having thus considered the general features of the ear, we may proceed 

 to a brief reference to the probable functions of its different parts. The 

 auricle or external ear collects and concentrates the sounds which fall upon 

 it ; and by the motion of the head and spine it can be turned in every 

 direction to receive them. The meatus auditorius conducts and reflects 

 I'rora its sides the sonorous undulations to the membrana tympani, which is 

 thereby thrown into vibrations, and these are transmitted by the chain of 

 bones to the membrana vestibuli, and partly to that of the foramen rotun- 

 dum, through the air and fluid which the tympanunl contains. The 

 Eustachian tube, by admitting air into this chamber, favors these vibrations 

 as well as the motions of the ossicula ; it may also allow the escape of such 

 sonorous impulses as strike on the walls of the labyrinth, and which might 

 produce an echo or confusion of sound. The mastoid cells may also con- 

 tribute to this effect as well as lighten the bone. Finally, the impressions 

 impinge on the membranous labyrinth on which the sentient nerves are 

 (expanded, and then convey the impressions to the sensorium. Sonorous 

 undulations, which strike the bones of the head and face, and the teeth, 

 are transmitted through these solid structures to the temporal bone, and 

 especially to the cochlea, on which numerous auditory nerves are ex- 

 I)anded. 



PI. 132, fig. 16, relation of the ossicles of the ear to the nerves which lie 

 between them : ', membrana tympani ; ", handle of the malleus ; ", process 

 of the incus ; ", tensor tympani ; ', chorda tympani. Fig. 17, Jacobson's 

 plexus ; a, promontory ; 6, portion of the mastoid process ; c, malleus ; d, 

 incus ; e, stapes ; fi fenestra cochleoe ; g, internal carotid artery ; Ä, Eusta- 

 chian tube ; z, tensor tympani ; a-, laxator tympani ; Z, Jacobson's nerve ; 

 m, a recurrent branch of do. ; «, branch to the fenestra cochleee ; o, con- 

 tinuation of the main trunk; ^5, inferior branch for the carotid artery; q^ 

 superior branch of Jacobson's nerve from which passes a thread, r, to unite 

 with the branch, s, to supply the Eustachian tube at t ; u, first thread to the 

 fenestra vestibuli ; v, second thread ; w, branch to the promontory and the 

 Eustachian tube ; x, end of Jacobson's nerve, as the superficial petrosal 

 which finally joins the otic ganglion. Fig. 18, bony labyrinth from above, 

 866 



