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 
numerous branches which anastomose with each other, and spread out into 
a delicate nervous membrane, or according to some, terminate in the form 
of papille. 
The facial or portio-dura nerve enters the meatus along with the audi- 
tory, and 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 corda tympani may be regarded either as 
the continued petrosal branch of the vidian, or as proceeding from the last- 
mentioned ganglion. It passes into the ear, winds among the tympanic 
bones, and escapes by a bony canal in the glenoid fossa. The tympanic 
plexus is a delicate network, chiefly formed by the tympanic branch of the 
glosso-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 
from 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 tympanum 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- 
panded. 
Pl. 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; °, corda tympani. Fig. 17, Jacobson’s 
plexus; a, promontory ; 6, portion of the mastoid process; c, malleus; d, 
incus; e, stapes; f, fenestra cochlee ; g, internal carotid artery ; h, Eusta- 
chian tube; 2, tensor tympani; 4, laxator tympani; J, Jacobson’s nerve; 
m, a recurrent branch of do.; n, branch to the fenestra cochlez ; 0, con- 
tinuation of the main trunk ; p, 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 ¢; w, first thread to the 
fenestra vestibuli; v, second thread; w, branch to the promontory and the 
Eustachian tube; z, end of Jacobson’s nerve, as the superficial petrosal 
which finally joins the otic ganglion. Fig. 18, bony labyrinth from above, 
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