ORGANS OF SENSE. 157 



PI. 132, ß.g. 1, left ear: u-e, helix; /-/c, antihelix; Z, tragus; in, anti- 

 tragiis ; ?i, lobe of the ear ; o, 2>, depressions between these elevations ; 

 q, concha. Fig. 2, muscles of the ear : a-e, cartilages of the ear ; f-p, ele- 

 vator or attollcns ; q-t, attrahens ; u-z, two retrahens. Fig. 3, small muscles 

 on the outside of the ear : ah c, greater ; def, smaller muscles of the helix ; 

 (/, /t, muscle of the tragus ; ?', ^, muscle of the anti-tragus. Fig. 4, muscle 

 of the inside of the external car : a-f, transverse muscles of the ear. Fig. 

 o, section, of the tympanic cavity : a, meatus opened ; 5, fossa on the inferior 

 wall of the meatus; c, fold for tlic membrana tjmipani ; c/, c?, tympanic 

 cavity proper ; e, entrance into the mastoid process ; /J cells of do. ; g, pro- 

 montory ; Ä, fenestra ovalis ; ?", Fallopian canal ; h, superior semicircular 

 canal ; /, mastoid process. Fig. 7, membrana tympani from the inside : a, 

 annular fold into Avhich it is fastened ; i, malleus ; c, elevation ; c?, o?, fibres 

 of which it consists. Fig. 8, ossicles of the ear in their proper positions : 

 a-d, temporal bone ; e, tympanic ring ; / malleus ; g, incus ; A, stapes. Figs. 

 9 and 10, malleus from two directions magnified: a, long process or gracilis: 

 i, short process ; c, manubrium ; c?, neck ; e, head ; g, articulating face for 

 the incus. Figs. 11 and 12, incus : /, body ; g, short process or erus ; /i, long 

 or inferior cms ; ^, os lenticulare ; h, articulating fiice for the malleus. Figs. 

 13 and 11, stapes: a, 5, head ; c, neck; deg, crura; / base. Fig. 15, tem- 

 poral bone .• a, &, Eustachian tube ; e, / tensor tympani ; g, h, t, stapedius 

 muscle. . 



C. Internal Far. 



This is the essential part of the organ of hearing. It lies 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 arc 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 Auditorius 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 varioiis minute foramina for the transmission of the nerves. 



2. The Vestibule, or central cavity of tlie 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. 

 r)n the tympanic side of the vestibule is seen the fenestra ovalis, closed by 



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