lyO THE SENSES OF ANIMALS 



outside flap or pinna that the word "ear" means in ordinary 

 talk. The flaps serve to protect the deUcate inner structures 

 and help to prevent foreign bodies entering the ear-tube. 

 They also serve as hearing trumpets for concentrating the 

 sound waves received, and for directing them down the tube. 

 In many mammals they are also highly movable and help 

 in locating the source of a sound when they are moved in 

 different directions. Our own ear-flaps are comparatively 

 small and immovable, and consequently we have to supple- 

 ment them with a cupped hand behind when we listen 

 attentively to faint sounds. 



Sound waves pass into the ear-tube from the pinna and 

 meet the ear-drum, a piece of thin skin that closes the tube 



MIDDLE EAR 



SEMICIRCUUR 

 CANALS 



COCHLEA 



Fig. 10. A diagram of the outer, middle and inner ear in man to show the 

 chief component parts. 



at its inner end. They make the ear-drum vibrate at the 

 same speed as their frequency, and are passed on and ampli- 

 fied by the structures on the other side. The inner side of 

 the drum forms part of the outer wall of a small cavity sur- 

 rounded by bone known as the middle ear. The cavity is full 



