Lab: Frog Dissection
Purpose: Study the external and internal anatomy of the frog.

Background info: As members of the class Amphibia, frogs may live some of their adult lives on land, but they must return to water to reproduce. Eggs are laid and fertilized in water.

dissecting tray
8 pins

Procedure & Identification Checklist:
1) Put on safety goggles and a lab apron.

2) Place a frog on a dissection tray. To determine the frog's sex, look at the hand digits, or fingers, on its forelegs. A male frog usually has thick pads on its "thumbs," which is one external difference between the sexes, as shown in the diagram below.

3) Use the diagram below to locate and identify the external features of the head. Find the mouth, external nares (nostrils), tympani (eardrums), and eyes.

_ mouth
_ external nares
_ tympani
_ eyes

4) Turn the frog on its back and pin down the legs. Cut the hinges of the mouth and open it wide. Use the diagram below to locate and identify the structures inside the mouth: the vomerine and maxillary teeth, the internal nares, the tongue, and the esophagus (food pipe)

_ vomerine and maxillary teeth
_ internal nares
_ tongue
_ esophagus

5) Insert the point of your scissors through the skin just above the anal opening and make an incision extending to the lower jaw. Make 2 horizontal incisions, open the skin flaps, and pin the skin flaps flat.

6) Make the same incisions as step 5 to cut through the muscles and breast bone. Pin the muscle flaps just like you did with the skin. NOTE: If your frog is a female, the abdominal cavity may be filled with dark-colored eggs. If so, remove the eggs so you can see the organs underlying them.

7) Observe the following organs

Layer 1:
_ Liver - large, brownish organ covering most of the body cavity
_ Heart - small triangular organ between front legs and above liver

Layer 2: Lift liver with forceps to see
_ Gall Bladder - small greenish sac under liver
_ Stomach - large, firm sac on left side
_ Small Intestine - long, folded tube smaller than and above stomach

8) Carefully remove the liver, heart, and gall bladder. Then observe the following organs

Layer 3
_ Lungs - small, reddish organs on either side of the heart

_ Pancreas - thin, yellowish ribbon between stomach and small intestine. Lift stomach to view.

9) Carefully remove the stomach, small intestines, and pancreas. Then observe the urinary and reproductive system.

_ Testes - tan, bean shaped organs
_ Ovaries - dark organ which may fill most of the body cavity

10) Dispose of your frog according to the directions from your teacher.

11) Clean all equipment and your work area. Wash your hands.