THE SENSES 4JJ 



flavored foods is found to dull the sense of t;iste. and ],v al(.<,],.,l .,t 

 least, the olfactories are rendered less acute." — Macv", / V///.svWoV//. 



The Organ of Hearing. -The organ of hearing is the ear. In a fi.h 

 irog, or reptile, the outer ear, so prominent in man, is entirely lacking Tl..^ 

 outer ear consists of a funnel-like organ composed largely „f cartilage whirli 

 IS of use in collecting sound waves. This part of the ear ind.xes the audi- 

 tory canal which is closed at the inner end by a tightly stretched membrane 

 the tympanic membrane. We have seen the tympanic membrane of the 

 frog on the outer sur- 

 face of the head. The 

 function of the tym- 

 panic membrane is to 

 receive sound waves, 

 for all sound is caused 

 by vibrations in the 

 air, these vibrations 

 being transmitted, by 

 the means of a com- 

 plicated apparatus 

 found in the middle 

 ear, to the real organ 

 of hearing located in 

 the inner ear. 



Middle Ear. — The 

 middle ear in man is 

 a cavity inclosed by 

 the temporal bone, 

 and separated from 



Section of ear, showing auditory canal, middle ear, internal 

 ear, and Eustachian tube. 



the outer ear by the tympanic membrane. A little tube called the Eusta- 

 chian tube connects the inner ear with the mouth cavity. By allowing air to 

 enter from the mouth, the air pressure is equalized on the ear drum. For 

 this reason, we open the mouth at the time of a heavy concussion and thus 

 prevent the rupture of the delicate tympanic membrane. Placed directly 

 against the tympanic membrane and connecting it with another mem- 

 brane, separating the middle from the inner ear, is a chain of three tiny 

 bones, the smallest bones of the body. The outermost is called the /jam- 

 mer; the next the incus or anvil; the third the stirrup. All three bones 

 are so called from their resemblances in shape to the articles for which 

 they are named. These bones are held in place by very small nujsch-s 

 which are delicately adjusted so as to tighten or relax the membranes guard- 

 ing the middle and inner ear. 



The Inner Ear. — The inner ear is one of the most complicated, as well 

 as one of the most delicate, organs of the body. Deep within the t<'m- 



