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 ; and 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 6, posterior portion of same ligament; x,x, 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. 



FIG. 4. Schematic representation of the perilymphatic and endolymphatic spaces. The former 

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

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

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

 cation at the helicotrema ; 11, aquseductus vestibuli ; 12, aquseductus cochlearis ; 13, periosteum; 14, dura 

 mater; 15, stapes in the fenestra ovalis ; 16, fenestra rotunda with its membrane. 



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