Explanation of Plate 1. 



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

 tensor tympani muscle (Testut): a, external auditory meatus; 6, tympanic cavity; c, vestibule of the 

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

 insertion of tendon of tensor t\ mpani ; 5, Long or vertical process of incus ; 6, head oi 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. 'J.— 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; l. base 

 ipes : 2, anterior border of fenestra ovalis ; 3, the pyramid ; l, tendon of stapedius muscle ; a, anterior 

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

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

 of the vertical line w Inch 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 scala-; C, lamina spiralis; /', 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; :'., semicircular canal : 4, 

 canalis cochlearis; . r >, ductus endolymphaticus with its two branches of origin ; 6, saceus endolymph- 

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

 cation at the helicotrema ; 11, aqua-ductus vestibuli ; 12, aqua ductus cochlearis : 13, periosteum ; 14, dura 

 mater; 15, stapes in the fenestra ovalis ; Ifi, fenestra rotunda w itli its membrane. 



