ORGANS OF SENSE. 157 
Pl. 182, fig. 1, left ear: u-e, helix; /-%, antihelix; /, tragus; m, anti- 
tragus; n,lobe of the ear; 0, p, depressions between these elevations ; 
g, concha. F%g. 2, muscles of the ear: a-e, cartilages of the ear; /-p, ele- 
vator or attollens; g-t, attrahens; u-z, two retrahens. vg. 8, small muscles 
on the outside of the ear: abc, greater; de/, smaller muscles of the helix ; 
g, h, muscle of the tragus; 7, &, muscle of the anti-tragus. Mig. 4, muscle 
of the inside of the external ear: a—/, transverse muscles of the ear. Fg. 
5, section of the tympanic cavity: a, meatus opened; 4, fossa on the inferior 
wall of the meatus; c, fold for the membrana tympani; d, d, tympanic 
cavity proper; e, entrance into the mastoid process; /, cells of do.; g, pro- 
montory; A, fenestra ovalis; 7, Fallopian canal; /£, superior semicircular 
canal; /, mastoid process. /%g. 7, membrana tympani from the inside: a, 
annular fold into which it is fastened; 6, malleus; c, elevation; d, d, fibres 
of which it consists. /%g. 8, ossicles of the ear in their proper positions: 
a-d, temporal bone; e¢, tympanic ring; f, malleus; g,incus; h, stapes. Migs. 
9 and 10, malleus from two directions magnified: a, long process or gracilis: 
6, short process; ¢, manubrium; d, neck; e, head; g, articulating face for 
the incus. gs. 11 and 12, incus: f, body; g, short process or crus; hf, long 
or inferior crus; 2, os lenticulare; &, articulating face for the malleus. igs. 
13 and 14, stapes: a, 6, head; ¢, neck; deg, crura; f, base. Mig. 15, tem- 
poral bone: a, b, Hustachian tube; e, f, tensor tympani; g, h, 2, stapedius 
muscle. 
C. Internal Ear. 
This is the essential part of the organ of hearing. It les deeply buried 
in the petrous bone, and consists of a number of curiously formed channels 
and spaces wrought out of the osseous structure, and containing delicate 
membranous tubes filled with fluid. On these the terminal branches of the 
sentient nerve are expanded. The internal ear or labyrinth consists of two. 
portions, an osseous and a membranous. ‘The osseous labyrinth consists of 
three distinct compartments: one in the centre, termed the vestibule; one 
behind this, composed ‘of three semicircular canals; and one in front of it, 
the cochlea. Both the anterior and posterior compartments communicate 
with the vestibule; and the meatus auditorius internus communicates 
with each of these by minute foramina for the transmission of the auditory 
nerve. 
1. Meatus Aupirogius INTERNUS is shorter and smaller than the ex- 
ternal. It is scarcely a quarter of an inch in length, and, lined by the 
dura mater, it leads from the cranium directly outwards, ending in a cul de 
sac, subdivided into two by a horizontal bony crest. In this depression are 
seen various minute foramina for the transmission of the nerves. 
2. THE VESTIBULE, or central cavity of the labyrinth, is a very small 
space placed between the fenestra ovalis and the meatus auditorius internus. 
Its form is very irregular, owing to dilatations in three directions, these bear- 
ing the names respectively of superior ventricle or cornu, inferior and pos- 
terior, and inferior and interior. In each cornu there are certain openings. 
On the tympanic side of the vestibule is seen the fenestra ovalis, closed by 
863 
