Preserved or freshly killed frogs in dishes or shallow pans of water; forceps and a bristle.
Observations.
Open the frog's mouth as widely as possible and, if necessary, insert a splinter to hold the jaws apart. Identify the following structures:—
Tongue. Draw it forward until the free end extends from the mouth and is outspread; observe its form, extent, and attachment. Teeth. Find those on the jaws and on the roof of the mouth. Nostrils. Push the bristle inward through a nostril to determine its direction and extent. Vocal cords. These form a hard white mass in the floor of the mouth, well back behind the tongue. Glottis, the slit inclosed [between] the vocal cords, opening into the trachea. Esophagus, the passage to the stomach, at the posterior end of the mouth. Eustachian tubes, small passages outward to the ears at the junction of the upper and lower jaws.
Questions.
- Describe the probable action of the frog's tongue in catching a bug.
- What advantage can you ascribe to the peculiar mode of attachment of the tongue?
- Of what use is the notch in the inner end of the tongue? (Note its position when the tongue lies at rest in the mouth.)
- If the frog chewed its food, how would the existing structure of the nostrils be very inconvenient?
- Recall either the frog's habit of feeding or the structure of the nostrils. Do you think the nostrils are of much service in smelling? State the reason for your answer.
- Of what use are the vocal cords and why are they so muscular? Consider their use in sound making and also their condition during swallowing.
- Of what use are the teeth? Recall the form and use of the fish's teeth.
Suggested drawings.
- The mouth, wide open and with tongue extended.
- A diagram showing the path of air and of food through the frog's mouth.