THE SPECIAL SENSES. 



141 



in their construction and articulate with perfectly formed 

 joints, one of which is a ball-and-socket joint. At the bottom 

 of the cavity is a small tube, leading from the middle ear to 

 the upper and back part of the pharynx. This passage keeps 

 up a supply of air to the middle ear. By holding the nose 

 and keeping the mouth closed, we can force air up this 

 It enters the ear with a sudden click. 



FIG. 44. Section through the Right Ear: M, outer ear; G, auditory canal; 

 T, the drum; P, middle ear; 0, bones of the ear; E, pharyngeal opening of 

 Eustachian tube ; V, vestibule; B, a semicircular canal; S, the cochlea; A, 

 auditory nerve. 



20. The Inner Ear. This chamber is somewhat com- 

 plex, and is sometimes called the labyrinth. It is situated in 

 a solid bone at the base of the skull, hollowed out for the 

 purpose, and consists of three portions the vestibule, or 

 antechamber, the semicircular canals, and the cochlea, or snail 

 shell. The vestibule, situated on the inner side of the drum, 

 is not larger than a grain of wheat. Above and behind are 

 three bony semicircular canals, which communicate with the 



