EXPLANATION OF PLATE 2. 



FIG. 1. Schematic representation of displacement of the auditory ossicles due to contraction of the 

 tensor tympani muscle (Testut) : a, external auditory meatus ; b, tympanic cavity ; c, vestibule of the 

 bony labyrinth; d, fenestra ovalis; 1, membrana tympani; 2, handle of malleus; 3, head of malleus; 4, 

 insertion of tendon of tensor tympani ; 5, long or vertical process of incus ; 6, head of incus ; 7, stapes. 

 (The arrow indicates the direction of traction of the tensor tympani muscle; ancl the lines in red indi- 

 cate the change in the position of the parts produced by it.) 



FIG. 2. Schematic representation of the displacement of the stapes due to contraction of the stape- 

 dius muscle (Testut) : A, the stapes in repose; B, stapes during contraction of stapedius muscle; 1, base 

 of stapes ; 2, anterior border of fenestra ovalis ; 3, the pyramid ; 4, tendon of stapedius muscle ; a, anterior 

 portion of annular ligament of stapes, longer than b, posterior portion of same ligament; x, a-, antero- 

 posterior diameter of fenestra ovalis, passing through the base of the resting stapes ; y, point of passage 

 of the vertical line which represents the axis of rotation of the stapes. 



FIG. 3. The three parts making up the bony cochlea (schematic, from Testut) : A, the columella; B, 

 spiral tube containing the scalse; C, lamina spiralis ; D, the three parts in their normal relations. 



..Foe, 4v-Seheaiic. representation of the perilymphatic and andolymphatic spaces. The former 

 appear in black, and the latter are colored blue (Testut) : 1, utricle; 2, saccule; 3, semicircular canal; 4, 

 canulis cochlearis ; 5, ductus endolymphaticus with its two branches of origin ; 6, saccus endolymph- 

 aticus ; 7, canalis reuniens; or canal of Hensen ; 8, scala tympani ; 9, scala vestibuli ; 10, their communi- 

 cation,at_the feelicatr-ema-; 11, aq-uaductus vestibuli ; 12, aqua;ductus cochlearis ; 13, periosteum; 14, dura 

 mater; 15, starpes irrthe fenestra ovalis ; 16, fenestra rotunda with its membrane. 



