Most digestion and absorption of food into the bloodstream takes place in the small intestine. Both bile and pancreatic enzymes flow into the small intestine. Digestive enzymes from the pancreas flows into this duct. Bile flows into a tube called the bile duct. Bile is a digestive juice made by the liver and stored in the gall bladder. Swallowed food moves from the mouth down the esophagus and into the stomach and then into the small intestine. INTERNAL ANATOMY: The digestive system consists of the organs of the digestive tract and the digestive glands. You may have to remove one side in order to continue your dissection. If your frog is female, the body cavity maybe full of black eggs. You will have to cut through the sternum (breastbone). BE CAREFUL NOT TO CUT TO DEEP AND DAMAGE THE UNDERLYING ORGANS. Now cut through the muscle layer and repeat the incisions you mad in step 2 and 3. Why are there so many blood vessels? Closed- circulation, double-looped circulation, allows blood to reach all parts of the frog’s body 4. Now make transverse cuts through the skin below each of the fore limbs and above each of the hind legs. With your scissors make a cut (through the skin only) along the midline of the belly from the pelvis to the throat. Place the frog on its dorsal side and secure it in place with dissecting pins through each of the legs. Maxillary Teeth: Used for holding prey 10. Nictitating Membrane: clear eyelid, protects the eye 9. Tympanic Membrane: eardrum, located behind eyes 8. ![]() Gullet: Opening leading to the esophagus 6.Tongue: Front attached, aids in grabbing prey 7. Eustachian Tubes: equalize pressure in inner ear 4. LOCATE and label THE FOLLOWING on Figure 2. Where does the eustachian tube lead? To the tympanic memebrane What is its purpose? Equalize pressure of the inner ear ![]() On both sides of the gullet, near the cut jaws are opening to the EUSTACHIAN TUBES. Find the GULLET (throat) it leads to the opening of the esophagus. It is the opening to the trachea (windpipe) that leads to the lungs. Locate a vertical opening toward the back of the mouth. The eyes help hold the prey as a frog is swallowing it. Push carefully on the eyes observe how they fill a space in the mouth. What are the maxillary teeth and vomerine teeth used for? To hold onto prey 9. They are located toward the front of the upper jaw and between the internal nares (internal nostril openings). Locate the 2 VOMERINE TEETH on the upper jaw. The teeth you feel are the MAXILLARY TEETH. Feel the inside of the upper jaw ( maxilla) and the lower jaw (mandible). Is it attached to the front or the back of the mouth? _Front_In a live frog, the tongue is sticky and is used to catch insects. Place the frog on its dorsal side in the dissecting pan and cut the corners of the mouth. Why does each sides color help protect the frog from predators? Coloration acts as camouflage Figure 1. Turn the frog onto its ventral side and notice the color difference. The frog can breathe directly through its skin as well as with its lungs. Label the mouth, tympanum, and the external nares on Figure 1. The nasal openings, are also call EXTERNAL NARES, found toward the tip of the snout will closes when the frog is under water. ![]() They locate the two openings into the nasal cavity. Behind each eye find the circular eardrum called a TYMPANUM. Label the eye and the nictitating membrane on Figure 1. It is a transparent membrane the protects the eye while permitting the frog to see under water. The 2 outer ones are the color of the fog's body. Label the hind and front legs on Figure 1. Notice the difference between the toes of the hind legs and those of the front legs. The forelegs provide balance and cushion the frog when it lands after jumping. The hind legs are strong and muscular and are used for jumping and swimming. Examine the hind legs and front legs of the frog. Place the frog on its belly (ventral side) in the dissecting pan 2. PROCEDURE AND OBSERVATIONS: EXTERNAL ANATOMY 1. Observe several frogs to see the difference between males and females. Male frogs are also usually smaller than female frogs. A male frog usually has thick pads on its "thumbs," which is one external difference between the sexes, as shown in the diagram below. To determine the frog’s sex, look at the hand digits, or fingers, on its forelegs. Purpose: In this lab, you will dissect an frog in order to observe the external and internal structures of the frog anatomy SEXING YOUR FROG: Place a frog on a dissection tray. FROG DISSECTION GROUP NAMES: _ Materials: Dissecting pins, forceps, scissors, paper towel, dissecting probe, preserved frog, dissection tray.
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