308 THE SPECIAL SENSES 



92. In those animals whose hearing is more delicate than 

 that of man, the corresponding organ is of greater importance, 

 it being larger, and supplied with muscles of greater power, 

 so that it serves as a natural kind of ear-trumpet, which is 

 easily movable in the direction of any sound that attracts the 

 attention of the animal. Bold, preying animals generally have 

 the concavity of this organ directed forward, while in timorous 

 animals, like the rabbit, it is directed backward. Fishes have 

 no outer ear, but sounds are transmitted directly through the 

 solid bones of the head, to the internal organ of hearing. 



93. The auditory canal (Fig. 70, A, 6), which is continuous 

 with the outer opening of the ear, is a passage an inch and 

 a quarter in length, its inner extremity being bounded by a 

 closely fitting, circular membrane. This canal is of oval form, 

 is directed forward and inward, and is slightly curved, so that 

 the inner end is ordinarily concealed from view. The pouch 

 of the skin which lines this passage is smooth and thin, 

 especially at the lower end, where it covers the membrane 

 just mentioned. 



94. As in the case of the nostrils, a number of small, stiff 

 hairs garnish the margin of the auditory canal, and guard it, 

 to some extent, against the entrance of insects and other for- 

 eign objects. The skin, too, covering its outer half, is furnished 

 with a belt of little glands which secrete a yellow, bitter sub- 

 stance, called " ear-wax," which is especially obnoxious to small 

 insects. As the outer layer of this wax-like material loses its 

 useful properties it becomes dry, and falls out of the ear in the 

 form of minute, thin scales, a fresh supply being furnished 

 from the little glands beneath. In its form, the auditory canal 

 resembles the tube of an ear-trumpet, and serves to convey the 

 waves of sound to the middle portion of the ear. 



95. The Middle Ear, or Tympanum. The middle ear is a 

 small cavity, or chamber, of irregular shape, about one-fourth 

 of an inch across from side to side, and half an inch long (see 



92. The ear in the animals of delicate hearing ? Rabbit? Fishes? 



98. What is the auditory canal ? Describe it. 



' 94. How is it guarded and protected ? " Ear-wax " ? 



95. What is the middle ear * Why called tympanum f 



