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._ 1. Describe the probable action of the frog's tongue in catching a bug. 2. What advantage can you ascribe to the peculiar mode of attachment of the tongue? 3. 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.) 4. If the frog chewed its food, how would the existing structure of the nostrils be very inconvenient? 5. 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. 6. 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. 7. Of what use are the teeth? Recall the form and use of the fish's teeth. _Suggested drawings._ a. The mouth, wide open and with tongue extended. b. A diagram showing the path of air and of food through the frog's mouth. The Organs of Digestion, Absorption, and Excretion _Materials._ Freshly killed or preserved frogs in dishes or shallow pans of water, forceps, and, if the pupil is to do any dissecting, scissors. _Directions and Observations._ The specimens may have been opened by the teacher, or may be dissected by the pupil as follows:-- Placing the frog on its back, with forceps firmly grasp the skin of the abdomen and the muscles beneath, just in front of the hind legs, and with the scissors cut straight forward in the middle line until the floor of the mouth is reached; this will separate the arms. Care must be taken not to cut too deeply, but this may be avoided by keeping the skin uplifted. Now cut sidewise in front of each hind leg in order that the body wall may be laid aside. Under the arms the heart will be seen; it will be studied as a part of the circulatory system. * * * * * Identify the following organs:-- _Liver_, the large red or brown mass, consisting of several divisions and lying close up under the arms. _Bile sac_, small, green, and between the liver lobes. _Alimentary canal._ 1. _Mouth._ 2. _Esophagus._