FROG DISSECTION ACTIVITY
Laboratory objective:
To observe the anatomy of a frog, understand its organ systems, and compare its structures to those of human.
Materials:
frog dissecting kit (pin, Dissection
safety goggles, gloves, scalpel, scissors, forceps, guide/worksheet
lab apron probe) Notebook for observation
dissection tray paper towels, plastic
storage bag
Safety Precautions:
1. Wear protetcive gear: Gloves, googles, and lab coats are essential.
2. Handle tools carefully: Use scalpels and scissors responsibly, always cutting away from your body.
3. Dispose of materials properly: Follow lab protocols for disposing of biological waste.
4. Wash hands after the dissection, even if gloves were worn.
Student Guide to the Frog Dissection Instructions
Part A - External Anatomy:
1. Make sure frog is right side up so that you can see the face.
2. Identify the eyes, which have a nictitating membrane that serves to moisten the eye.
3. Identify the tympanic membrane, or eardrum. It is located behind each eye. (Look at Figure 1)
4. Find the external nares or nostrils. (Look at Figure 1)
5. Find the digits, which are like fingers on both the fore and hind limbs. (Figure 2)
6. Determine if your frog is male or female by looking at the innermost finger of the forelimb. The male pad is an
enlarged darker patched pad that the male uses to grasp a female during mating. (Figure 2)
Part B - Mouth:
1. Pry open the mouth. Use the scissors to cut the corner
of the mouth where the maxilla (upper jaw) and mandible
(lower jaw) join together.
2. Find the tongue and pull it out.
3. Feel the maxillary teeth that are along the rim of the upper jaw.
(Look at Figure 3).
Notice that only the upper jaw has teeth.
4. Locate the glottis (Figure 3).
It is a slit opening for the voice box on the floor of the mouth.
5. Find the esophagus (Figure 3) at the rear of the mouth.
Part C – Internal Anatomy: Dissection
Opening up the frog: (Figure 4)
1. Place the frog ventral side up (on its back) and pin its four limbs down
2. Lift the frog’s skin with forceps between the rear legs.
3. Make a small cut through the lifted skin with the scalpel.
Take care to cut only the skin. You are making a starting
place for the scissors.
4. Use the scissors to continue the incision up to the
midline all the way through the frog’s skin.
5. Stop cutting when your scissors reach the frog’s neck.
6. Now, you will cut horizontally. Use the scissors to
make sideways incisions in the skin
7. The first incisions are made between the front legs.
Then do the same with the rear legs.
8. Be careful to cut only skin, not muscle.
9. Pick up the flap of skin with the forceps.
10. Use a scalpel to help separate the skin from the
muscle layer below. Then pin the skin to the dissection tray.
Cutting the Muscle and Bone;
First muscle incision:
1. Do the same incisions, this time through the abdominal muscle.
You will find it easier to begin the vertical incision by lifting the muscle layer with the forceps.
Do this between the rear legs of the frog.
2. Make a small cut with the scalpel.
3. Use the scissors to continue the incision up the middle to just below the front legs.
4. Don’t cut too deeply, the muscle is thin. It is easy to damage the organs underneath.
Cutting the bone:
5. Cut through the chest bones. When you reach the point just below the front legs, turn the scissors blades
sideways, so that you only cut through the bones in the chest. Be careful that you don't cut too deeply.
6. Stop cutting when your reach the frog’s neck.
Second (Horizontal) Muscle Incision:
7. Make the horizontal (sideways) incisions, just as you did with the skin using the scalpel. The first incision
is between the front legs, the second is between the rear legs.
8. Separate the muscle flaps from the organs below. Pull back and hold the muscle flaps with the forceps.
9. Use scalpel to separate the muscle from the organ tissue.
10. Pin the muscle flaps back far enough to allow easy access to the internal organs.
Part D – Internal Body Systems:
1. We are now ready to explore the frog's anatomy.
To make our exploration easier, we will look at the organs in four different layers, beginning with the
liver and heart layer.
Layer 1
2. The liver is a large, brownish colored organ covering most of the body cavity.
3. The heart is a small triangular shaped organ between the front legs, just above the liver.
Layer 2
5. Reveal layer two. The heart and liver in layer one hide some of the organs below them.
6. Use the forceps and the probe to pick up the liver and reveal layer two.
7. Layer two includes the gall bladder, the stomach, and the small intestine.
8. Examine the gall bladder. Under the liver, we see a small, greenish sac. This is the gall bladder.
You might also see it by separating the right and middle lobes of the liver.
9. Examine the stomach. The stomach looks like a sac on the frog's left side (on your right).
It is a large firm organ.
10. Examine the small intestine. The small intestine is a long folded, tube like organ, that is posterior the
stomach.
Layer 3
11. Reveal layer three. Remove the liver to see the organs in layer three.
12. The liver is easier to remove if you remove the gall bladder and heart at this time. Put to the side, but
still on the tray.
13. Take a close look at the lungs and pancreas. The lungs are difficult to locate in a preserved frog.
They are on either side of the heart.
14. You may need to remove the lungs and place them on the tray as well.
15. You can't see the pancreas without lifting the stomach and intestines with the forceps.
The pancreas is a thin, yellowish ribbon.
16. The intestines are held in place by thin, transparent tissue called the mesentery.
17. If you have a female frog, you will need to remove the ovaries before you can see layer four.
Place the organs in the tray.
Layer 4
18. To see layer four, you need to remove the stomach, small intestine, large intestine, and pancreas. Place
on the tray.
19. Examine the spleen. Locate the spleen in the male frog. It is a small, round reddish organ. It is a little
more difficult to find the spleen in a female frog
20. The kidneys are elongated, brownish colored organs found in the lower part of the frog's abdomen.
21. Female kidneys are located in the same place but can only been seen after removal of the ovaries and
oviducts.
Clean Up!
Clean up your work area and equipment. Return the cleaned dissecting equipment to the appropriate place.
ABDOMINAL AND CHEST CAVITIES OF THE FROG
Label the Diagram.
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B. __________________________________
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H. __________________________________
I. __________________________________
J. __________________________________
K. __________________________________
L. __________________________________
M. __________________________________
N. __________________________________
Name: ______________________________________ Section: ___________ Date: ____________
Conclusion Questions – Independent work
(Answer in complete sentences).
1. Did you have a male or female frog? How did you identify this fact? (be specific as to how you can tell the
difference)
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2. Where is the frog’s liver located and what is the purpose of this structure?
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3. How are the feet of the frog adapted to swimming?
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4. How does the length of the small intestine relate to its function in absorbing digested food?
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5. The frog’s heart is different than the human heart – describe the differences you saw. Later, research the differences
and write a paragraph summarizing the differences. Make sure to provide a reference stating where you got your
information.
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