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 ments in breathing. Can you find how often it breathes per minute? Place hand under the bird's wing. What do you think of its temperature; or better, what temperature is shown by a thermometer held under its wing? Do you see any connection between the breathing rate and the temperature? Test (as with the crayfish) whether a bird can see behind its head? Notice the movements of the nictitating membrane. Does it appear to be transparent?

Watch a bird fly around a closed room and review the questions on Control of Flight.

Bend a bird's leg and see if it has any effect upon its toes. Notice a bird (especially a large fowl) walk to see if it bends its toes as the foot is lifted. Pull the rear tendon in a foot cut from a fowl for the kitchen. Does the bird have to use muscular exertion to grasp a stick upon which it sits? Why, or why not? When is this bending of the toes by bending the legs of special advantage to a hawk? To a duck? A wading bird? Why is a fowl safe from a hawk if it stands close to a tree?

c, tongue; a, b, d, hyoid bone; e, q, windpipe; f, salivary gland.

Do you see any signs of teeth in the bird's jaws? Why are duck's "teeth" (so called by children) not teeth? Can the tongue of a bird be pulled forward? (Fig. 303.) What is its shape? If there is opportunity, dissect and study the slender, bony (hyoid) apparatus to which the base of the tongue is attached (Fig. 303), the opening of the windpipe, or trachea, the slit-like opening of windpipe which is so narrow as to prevent food falling into the windpipe.