THE VERTEBRATE BODY 



327 



ous organs can detect the presence of extremely minute quantities of 

 substances which we inhale along with the air we breathe. Some 

 vertebrates, such as dogs, have a much larger patch of olfactory sense 

 organs and, hence, have a much keener sense of smell than man or a 

 frog. 



The sense of taste is recorded by taste buds which are chiefly on the 

 tongue. There are four main kinds of these which detect salt, sour, 

 sweet, and bitter, respectively. Other properties which are associated 

 with the flavor of foods are due to the odor, temperature, and texture of 

 the foods as they are being eaten. 



Photo by Winchester 



Fig. 22.18. The semicircular canals from the internal ear of the dogfish shark. These 

 are similar to the ones found in man, but are much easier to dissect out in the shark 

 because they are embedded in cartilage rather than bone. The letters indicate the an- 

 terior-posterior vertical, the lateral vertical, and the horizontal semicircular canals. 



The sense of hearing is localized in the ear. Sound vibrations are 

 picked up by a tympanic membrane, transferred through the ear bones 

 of the middle ear to the fluid found in the inner ear. Here are found 

 the nerve endings which transmit the vibrations of different rates into 

 impulses which go to the brain and give the impression of sounds of 

 different tones. The tympanic membrane of the frog lies just back of 

 the eye — in man it is at the bottom of an auditory canal which leads in 

 from the outer portion of the ear. 



