Dissection of a Rana catesbiana (Bull Frog) - Procedure

Day 1: Examining the Skeletal, Muscular and Integumentary Systems.
1. Once you have been assigned a lab partner, obtain your safety equipment (gloves, apron, and goggles) and a lab notebook..
2. Next, see you teacher to gather your dissecting tools: a razor, dissecting scissors, dissecting probe, forceps, a dissection tray, and a dissecting pins.
3. Once all of your supplies have been gathered, your teacher will distribute the preserved bullfrogs to each group.
4. Place your frog onto the dissection tray, examine the frog’s forelimbs (front legs) and hind limbs (back legs) and describe the color, texture and other features in your notes.
5. With your scissors, make a small cut in the skin around the frog’s hip joint, where the hind legs meet the torso. Use your razor blade to make a circular cut around the leg, being careful not to cut any muscles or tendons beneath the skin. With the forceps, peel the skin off the hind limb to see the muscles, bones, and connective tissue underneath.
6. Observe and note the interconnected functions of the bones, muscles and tendons.
7. In your lab notes, diagram and label the muscles and bones using the appendix to the lab manual to identify them.
8. Discard the removed skin. Place the frog in a plastic storage bag and write your groups name on it. Then clean off your lab area, including all utensils and the dissecting tray. Hang up your apron, put away your goggles and finally discard your gloves.

Day 2: Examining the Cardiovascular and Respiratory Systems
1. Begin by gathering all of your supplies and safety equipment. Then find your frog and remove it from the storage bag. (Be sure to keep the bag for further storage.)
2. Lay the frog on its back on the dissecting tray and use the dissecting pins to secure its limbs to the tray.
3. Lift the loose skin near where the frog’s hind limbs meet its torso and make a cut here with the scissors.
4. Being careful not to cut deeper than the skin, make a cut along the top and bottom of the frog’s torso, from left to right. Then make a third cut, connecting these two cuts, along the center of the frog’s body (from head to tail. This should create two flaps of skin, which can be pinned to the dissecting tray to reveal the muscles of the torso. Draw and describe these muscles in your notes.
5. Next, cut the muscles of the body in the same pattern that you cut the skin. Be very careful not to cut deeply, as this will damage the internal organs of the frog. When you reach the forelimbs, you will have to cut through the frogs sternum and ribs. Again, you should now be able to pin these muscle flaps to the dissecting tray, exposing the internal organs.
6. Determine if your frog is male or female using the diagrams in the appendix to the lab manual, and write this into your notes section. (The most common sign that the frog is female is the presence of black and white eggs, and yellow fat bodies, covering the internal organs. If these are there, remove and discard them.)
7. Find the reddish triangular heart in the middle of the upper body. The frog heart has two atria and one ventricle, find these and the major arteries and veins. Describe them in your lab notebook.
8. Locate the pair of spongy-textured lungs on either side of the heart. Draw, label and describe them in your lab notebook.
9. Carefully remove and discard the heart and lungs, without damaging any of the other organs.
10. Re-store your frog in its plastic bag and return it to its storage place. Clean all of the utensils, the dissection tray, and your lab table. Finally, remove and return your safety equipment.

Day 3: Examining the Digestive and Excretory Systems
1. Begin by gathering all of your supplies and safety equipment. Then find your frog and remove it from the storage bag. (Be sure to keep the bag for further storage.)
2. Lay the frog on its back on the dissecting tray and use the dissecting pins to secure its limbs and chest flaps to the tray.
3. Open the frog’s mouth and use your scissors to cut the edges of the mouth at each hinge joint. Now you should be able to fully open the frog’s mouth and observe the internal structures.
4. Using your dissecting probe, locate the external nares (holes the frog breathes through) and follow the opening into the frog’s mouth. Note the location of both nares in your lab notebook.
5. Locate and describe the frog’s maxillary teeth (along the rim of the mouth) and vomerine teeth (further back in the mouth). Draw and label these in your lab notebook.
6. Find the wide opening at the center of the mouth. This is the top of the esophagus and below the esophagus is a slit called the glottis, which leads to the lungs.
7. Use the dissecting probe to move the frogs tongue. Describe the tongue’s texture and location in your lab notebook.
8. Now look inside the body cavity. Find the place where the esophagus attaches to the mouth. This is where you will begin looking at the digestive system. Draw, label and describe each organ in your lab notebook as you find it.
9. Follow the esophagus to a large, ‘ J ‘ shaped structure, this is the stomach. Above the stomach in the middle of the body cavity is a large, reddish-brown organ, this is the liver. Remove the liver and set it aside.
10. Under the liver, look for a greenish sac called the gall bladder.
11. Look back to the stomach, at the end of the stomach you will find the beginning of the frog’s intestines.
12. Just above the stomach, look for a thin ribbonlike organ, this is the pancreas.
13. Gently lift and remove the gall bladder, pancreas, stomach and small intestines. Notice that the end of the small intestine is attached to a larger tubelike organ, this is the large intestine, which leads to the cloaca (the organ that passes waste from the body).
14. Carefully remove the remaining digestive organs. Discard the removed organs and store your frog in its bag again. Clean all your utensils and lab area before putting away your safety equipment.


Day 4: Examining the Nervous System
1. Begin by gathering all of your supplies and safety equipment. Then find your frog and remove it from the storage bag. (Be sure to keep the bag for further storage.)
2. Lay the frog on its front on the dissecting tray and use the dissecting pins to secure its limbs to the tray.
3. Using your razor, cut away the skin along the spine of your frog. Peel the skin back and carefully remove muscle surrounding the spinal column. Note the structure of the vertebral column and record it in your lab notebook.
4. Carefully insert the point of your scissors into the underside of a neutral arch of one of the vertebral bones and cut. Press on the sides of the vertebra and expose the spinal column. Observe and note in your notebook.
5. Remove the skin from the frog’s skull to expose the cranium. On either side of the skull, use your scissors to cut the cranial bone from back to front. Carefully remove the top of the skull to expose the brain. Note the location of the brain and optical nerve and describe in your lab notebook.
6. Once you have recorded all of your observations, you can now discard the remainder of your frog.
7. Thoroughly clean all of your dissecting tools and put them away properly.
8. Put away your safety equipment and clean the lab.