176 PHYSIOLOGY AND MORPHOLOGY OF ANIMALS. 



Ossicles. — Running across from the membrane of 

 the drum to the foramen ovale is a chain of three little 

 bones, called the malleus (hammer), the incus (anvil), 



St. in. m. 



Fig. iio. — Ossicles, enlarged: st, stapes; in, incus; m, malleus. 



and the stapes (stirrup). These are articulated together 

 and to the walls of the cavity in a somewhat intricate 

 way, but evidently contrived to carry vibrations of the 

 drumhead to the interior ear, for the malleus is attached 

 to the drumhead, the stapes to the membrane of the 

 foramen ovale, and the incus is intermediate. Sound 

 vibrations of the air cause corresponding vibrations of 

 the drumhead (/), and these are carried along the chain 

 of bones and shake the membrane of the oval opening, 

 and therefore the water filling the inner ear, where its 

 further effects will be given after the inner ear is de- 

 scribed. The actual shapes of these bones are shown 

 in Fig. no. 



Interior Ear, or Labyrinth. — The real receptive 

 part of the ear is here. All other parts are purely in- 

 strumental. It is called the labyrinth because of the 

 complex winding passages in which the branches of the 

 auditory nerve are distributed. The labyrinth may be 

 best described under two heads, viz., the bony labyrinth 

 and the membranous labyrinth. The bony labyrinth 

 consists of winding cavities in the solid bone ; the mem- 



