THE SPECIAL SENSES 



253 



or auricle, and of a tube about an inch long, called the audi- 

 tory canal. 



The auricle is used as a kind of ear trumpet to gather up 

 the sound waves. Many animals are able to move the 

 large external ear in the direction of the sound. Thus, the 

 horse and the rabbit prick up their ears when they hear a 

 noise, the better to judge of the direction of sounds. 



The auditory canal is a passage in the solid portion of the 

 temporal bone. It is lined by skin on which there are fine 

 hairs, and a set of glands secreting earwax, which serves 

 to moisten the parts, catch particles of dust, and keep 

 away small insects. 



The inner end of the auditory canal is closed by a mem- 

 brane stretched tightly across it. It resembles the parch- 

 ment stretched across the end of a drum, and is known as 

 the tympanic membrane, or drum membrane. 

 It is thin and elastic, but may be broken 

 by a blow, or by pushing some sharp or 

 hard substance into the ear. 



347. The Middle Ear. The middle ear 

 is a small, drumlike cavity, 

 full of air, in the temporal 

 bone. This cavity is 

 known as the drum of the 

 ear, or tympanum. On the 

 inner wall of this air cham- 

 ber are two small openings, 

 the "oval window" and the "round window," both of which 

 are closed by membranes. The most curious feature of the 

 middle ear is a string of three tiny bones which stretch across 

 it. These bones are called from their shape the hammer, or 

 malleus ; the anvil, or incus; and the stirrup, or stapes. 



FIG. 156. A Cast 

 of the External Audi- 

 tory Canal. (Poste- 

 rior view.) 



