EXERCISE 64 



Problem. How does the frog breathe ? 



What to use. A live specimen in a battery jar, or a freshly killed specimen ; straw ; dissecting 

 needle ; glass tube drawn out almost to a point. 



What to do. Locate the nostrils and observe their movements during the breathing process. Note the 

 movements of the floor of the mouth, under the jaw. Watch the frog as he seems to swallow and also 

 watch the throat and the nostrils during this process. Observe the sides of the animal and see if you 

 can correlate the various motions ; that is, do the sides puff out when the throat puffs out or when 

 it contracts ? 



On a freshly killed specimen note by probing with a straw where the nostrils lead. Does this help 

 you to decide why the throat puffs out ? At the rear of the mouth locate a raised spot, and with the 

 dissecting needle pull one side away from the rest, thus disclosing a narrow slit, the glottis, in the 

 middle of the elevation. Gently insert the glass tube in the glottis and, by blowing, inflate the lungs. 

 Does this help you decide why the animal's sides puff out ? Dissect out the lungs and the tubes that 

 connect them, noting where the tubes (bronchi) join and form the trachea and where this one tube 

 enters the mouth. 



Record. Draw a picture of the nostrils and the lungs and tubes. 



Questions. 1. Tell how air enters a frog's mouth. 



2. How is air forced into the lungs ? 



3. How is air expired ? 



NOTE. The frog has no diaphragm as have human beings and other mammals. 



4. What does the work of this structure ? 



5. What would happen if a frog's mouth were kept open indefinitely ? Why ? 



6. How does the frog breathe when buried in the mud in winter ? 



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