Frog Dissection

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External Frog Anatomy

1. Obtain a preserved frog and place it on your dissecting tray, dorsal surface up.
2. Notice the appendages developed for a terrestrial life. The frog is a tetrapod, meaning that it possesses 4 limbs for locomotion. Observe that each forelimb is divided into an upper arm, forearm, and hand. Each hind limb is divided into a thigh, lower leg, and foot.
3. Study the head’s external features.
   1. Find the 2 external nares at the head’s tip. They are used for respiration.
   2. Posterior to the eyes are round tympanic membranes, the frog’s external sound receptors.
4. Study the eyes. Notice the cloudy eyelid attached at the bottom of each eye. This is the frog’s third eyelid, the nictitating membrane. In a living frog, this membrane is clear. It moistens and protects the eye.
5. Locate the cloaca at the specimen’s posterior end. The cloacal opening, or anus, is the single exit from the urinary, reproductive, and digestive systems.
6. Place the frog on its dorsal side.
7. Cut through the jaw joints on each side of the mouth and open the mouth wide.
8. Identify the glottis and the opening to the esophagus. The esophagus leads to the stomach, and the glottis to the lungs.
   
   
   
   
9. There are 2 sets of teeth. The fine maxillary teeth line the upper jaw and the two prominent vomerine teeth are found behind the mid-region of the upper jaw.
10. Two openings can be seen on the lateral sides of the mouth’s roof. These are openings to the Eustachian tubes, leading to the tympanic membranes. These tubes help equalize pressure.

Internal Frog Anatomy

1. Lay the frog ventral surface up on the dissecting tray.
2. Pinch the loose skin at the center of the frog’s stomach and make an initial cut with the scissors into the skin.
3. Cut through the skin, following the pattern shown in the diagram below.
   
   
   
   
4. Follow the same pattern to cut through the muscle and reveal the internal organs.
5. Find the large brownish structure in the center of the body cavity, the liver. This is the largest internal organ that consists of 3 lobes.
6. Lift the lobes of the liver and locate the gallbladder. It is a small greenish sac that stores bile.
7. Use the labeled diagram below to explore the rest of the internal anatomy. Identify the following internal structures:
   1. Stomach
   2. Small intestine
   3. Large intestine
   4. Spleen
   5. Heart
   6. Lungs
   7. Fat bodies
      
      
      
      
8. Follow all clean up and disposal instructions.