Frog Dissection
Objectives:
• To observe the external and internal anatomy of a frog.
• To determine the sex of a frog using internal anatomy.
• To view the body systems and determine which systems are like humans.
Hypothesis/Pre-Lab Questions:
1. Do frogs have teeth?
2. Do frogs have gills, lungs, or both?
Procedure:
EXTERNAL ANATOMY
1. Measure the length of the frog in cm. Record this measurement in Table 1.
2. Sketch the dorsal side of the frog. This is Figure 1. Label the following: Dorsal,
Anterior, Posterior, Eye, Nostril, Tympanum, Foreleg, Hind Leg, Mouth,
Anus, Chromatophores.
3. Sketch the ventral side of the frog. This is Figure 2. Label the following:
Ventral, Anterior, Posterior, Mouth, Anus, Foreleg, Hind Leg.
4. Locate the nictating membrane.
5. Open the mouth of the frog and examine the following structures: Throat,
Tongue, Teeth, Nostrils (Push probe through the nostril by pushing the probe
from the outside to the inside of the mouth), Glottis (the bubble like structure in
the back of the throat.
INTERNAL ANATOMY
SKETCH THE INTERNAL ORGANS OF THE FROG AND LABEL THEM AS YOU
COMPLETE #1-25.
6. Place the frog ventral side up.
7. Take scissors and snip the skin above the anus. You will have to use the scissors
to cut the skin. (See Fig.2 on Dissection Techniques handout). Use the probe to
tear away skin from the muscles.
8. Remove the skin from the frog. Locate the following muscles: Deltoid,
Pectoralis, Rectus abdominus, Gastrocnemius.
9. Carefully cut through the muscles of the abdomen the same way as you cut the
skin.
10. Pin open the skin and muscles to see the internal organs. If your frog is a female,
it will have egg masses covering the organs. Remove the eggs.
11. Locate the fat bodies that are located on both sides of the organs. They are long,
yellow structures.
12. Locate the yellowish testes or white ovaries. They are located below the fat
bodies. Record the sex in Table 1.
13. Remove the fat bodies and the testes or ovaries once you found them.
14. Locate the liver. Use the forceps to lift the liver and locate the gallbladder. I t
will be a bag like structure under the lobe of the liver. Once you have observed
these organs remove them.
15. Locate the stomach. Lift the stomach and locate the pancreas. It is a small
organ in the membrane of the intestine near the stomach.
16. Cut a slit in the stomach and examine the contents inside. Remove the stomach
and pancreas once you have made observations.
17. Locate the small intestine. Follow the small intestine to the large intestine.
Above the large intestine is the bladder, which empties into the cloaca.
18. Notice the intestines are held in place by a membrane called mesentery. Cut
through the mesentery with the probe and straighten out the intestine. Measure
the length of the small intestine in cm and then measure the length of the large
and small intestine in cm. Record the measurements in Table 1.
19. Remove the intestines, cloaca, and bladder.
20. Locate the kidneys. They are located on either side of the backbone and are
reddish –brown in color.
21. Locate the heart. Lift up the heart and locate the major arties (will be filled with
latex).
22. Sketch a drawing of the heart. This is Figure 4. Remove the heart and cut it in
half with scissors, after you make the drawing. Locate the three chambers.
23. Locate the lungs. They are dark red in color and located in the upper chest region
on the right and left side of the heart.
24. Remove the lungs once they have been observed.
25. Unpin your frog and pin it dorsal side up.
26. Snip the skin above the brain if it still present. Scrape away or chip away the bone
between the eyes until the brain is revealed. BE CAREFUL! The bone is very
thin.
27. Look at any frog structures that you want under a dissection microscope.
28. Dispose of frog and clean up!
Data:
Drawings that should be included in your lab report.
Figure 1 – External Dorsal View
Figure 2 – External Ventral View
Figure 3 – Internal Ventral View
Figure 4 – The Heart
Table 1
Length of Frog
Sex of Frog
Length of Small Intestine
Length of Large Intestine
Total Length of Intestine
cm
cm
cm
cm
cm
Analysis Questions:
1. Typically, how long is the average human intestine?
2. How many chambers are there in a human heart?
3. How many chambers are there in a frog heart?
4. List the structures located in the frog’s internal body that are NOT in
humans.
5. List the structural parts of a frog that are similar, external and internal,
to humans.
Conclusion:
Restate all hypotheses and explain if each is correct or incorrect.
Successfully prove knowledge of objectives was gained.
These are the objectives of the lab. Make sure to prove you gained knowledge about them.
-To observe the external and internal anatomy of a frog
Hint- pick 4-5 interesting things discovered from dissecting and inform the
reader about them.
-To determine the sex of a frog using internal anatomy.
Hint: explain to the reader how to determine a male and a female frog.