Download part 1—external anatomy

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FROG DISSECTION—Rana pipiens
PART 1—EXTERNAL ANATOMY
Follow these instructions carefully. Answer the questions using complete sentences on a separate
sheet of paper.
1. Look at the frog’s head. Find the eyes, mouth and nostrils (nares). Look behind and below the eye and
find the tympanic membrane. What do you think is the function of the tympanic membrane?
2. Look at the large, protruding eyes. (a) Why is the position of the eyes an advantage to the frog?
Observe the eyelids. (b) How are the eyelids different from humans?
3. Notice that the frog has no neck. How might this be a disadvantage to the frog?
4. Decide if your frog is male or female. Look on the inside of the thumb on either front limb. A male frog
has a large, black swelling on the inner side of the thumb. There is no such swelling in female frogs. Be
sure you can tell the difference. Is the frog you are working with male or female? Explain how you
know.
Open the frog’s mouth. You may have to cut through the skin and bones on both sides where the
jaw joins the skull. Refer to the drawing on the back of this sheet.
5. Rub your finger along the edges of the upper and lower jaw to locate the small teeth. Which jaw has
teeth? These teeth are called maxillary teeth. Notice that they slant inward. How would this help a frog
in capturing its food? (Keep in mind that frogs eat live insects.)
6. Find the vomerine teeth. These are located in two groups on the anterior (front) portion of the roof of
the mouth between two holes. How would these teeth be useful to the frog?
7. Find the internal nostrils. These are the holes on each side of the vomerine teeth. Pass a probe into the
external nostrils toward the posterior region. The probe should come through the internal nostril. What is
the function of the nostrils?
8. Find the openings of the Eustachian tubes. There is one on each side of the posterior portion of the
mouth near the angles of the jaws. Carefully pass a probe into one of the Eustachian tubes and see where
it goes. (a) Where does the probe go? (b) What is the function of the Eustachian tubes? (Consider
how sometimes your ears pop.)
9. Find the tongue. (a) Where is it attached to the mouth? (b) How does a frog use this way of
attachment in catching food?
10. Look into the back of the frog’s mouth, the pharynx. Find the opening of the esophagus. Look in the
posterior, central portion of the pharynx. To what system does the esophagus belong?
11. Find the glottis. This is the entrance to the lungs. Look for a round lump on the floor of the mouth
between the tongue and the esophagus. There is a slit in the middle of this lump that is the glottis. Does
food or air pass through the glottis?
Maxillary Teeth
External nostril
Internal nostrils
Eye
Eyelid
Vomerine teeth
Tympanic membrane
Esophagus
Eustachian tube
Glottis
Tongue
FROG PART
COMPARISON TO HUMAN
FUNCTION
Nostril
(external)
Nostril
(internal)
Teeth
(location & type)
Eye position
Eyelid
Ear
(tympanic membrane)
Tongue
(attachment)
Eustachian tube
Equalize pressure between
inner ear and outside air
PART 2—INTERNAL DISSECTION
Beginning at the posterior end of the ventral side, cut through the skin right up the middle of the frog’s
belly to the tip of the chin. Make a similar cut through the thin layer of muscle under the skin. You will
need to cut deeper between the front limbs to get through some bone. At each end of the long incision,
make a cut toward each side of the frog’s body. This will create two large flaps in the body wall. Pull the
flaps open and pin them away from the frog’s body.
12. Observe that the body wall is made of three layers: the skin, the muscle layer and the peritoneum.
The peritoneum lines the body cavity that contains the internal organs. Notice the blood vessels on the
inside of the skin. We have much thicker skin with a layer of fat under it (like the chicken skin) (a) What
is the function of the thin skin with blood vessels near the surface? (b) What advantage does the
thin skin have for the frog as compared to thick human skin? (c) What is the advantage of the thick
skin for a human?
13. Locate the heart a reddish-brown and tan structure in the middle of the anterior region between the
front limbs. Cut the heart open. Notice the frog has 3 chambers…the human has 4. A four chamber heart
is more efficient at getting oxygen to the cells. How can the frog survive if it doesn’t have as efficient
of a heart as ours?
14. Locate the liver. It is right below and surrounding the heart. The liver has three lobes. Which lobe is
the largest: right, left or middle?
15. Find a small greenish sac attached to the middle lobe of the liver. This is the gall bladder. The gall
bladder stores a chemical called bile that helps dissolve fat (like dish detergent) in the digestive system.
Why does an animal need bile to help dissolve fat?
16. Find the lungs. These are two thin-walled, reddish-brown sacs located below the heart and liver. (a)
What opening in the mouth connects to the lungs? Place an eye dropper in the glottis (located in the
mouth), squeeze the eye dropper. (b) What happens to the lungs? The frog’s lungs are much smaller in
relation to the body than human’s lungs. (c) Why do humans need bigger lungs?
17. Find the stomach. It is a curved, white structure. Cut open the stomach along the outside curve. (a)
Can you tell what the frog had for its last meal? (b) Describe the appearance of the stomach lining.
18. Lift the left lobe of the liver and find the esophagus. Measure the length of the esophagus by placing
the dull probe down the esophagus opening in the mouth and look for it at the top of the stomach. (a)
How long is the esophagus? (cm). (b) What is the function of the esophagus?
19. See the small intestine, the main organ of digestion, leading from the other end of the stomach. (a)
Describe the shape of the small intestine. (b) What else do the small intestines do?
20. At its posterior end, the small intestine empties into the larger large intestine. The large intestine, also
known as the colon, has three regions in humans. How does this compare to the frog?
21. Find the mesentery. It is a thin, transparent membrane that suspends the digestive tract from the dorsal
body wall. Carefully lift the mesentery around the small intestine and observe the dark brown blood
vessels. What specific function do these blood vessels have?
22. Find the kidneys. Look underneath the digestive tract for a pair of flat, dark, reddish-brown structures
lying along the middle of the dorsal region. Human kidneys are shaped like kidney beans. (a) What is the
function of the kidneys? (b) How many kidneys does a human have?
23. The urinary bladder is a clear sac located below the kidneys. What is the function of the urinary
bladder?
24. Find the yellow, finger-like projections above the kidneys. These are the fat bodies. Humans do not
have fat bodies. Much of our fat is under the skin. Fat provides stored energy. The frog has large fat
bodies in the summer and fall and much smaller ones in winter and spring. What is the function of the
fat bodies in the frog?
25. Find the reproductive structures. A male will have small, oval cream-colored testes located at the
base of the fat bodies. A female will have coiled oviducts and ovaries (either filled with black and white
eggs or empty and fan-shaped) attached at the top of both kidneys. Is your frog male or female?
27. Humans have a muscular sheet that separates the chest from the abdominal cavity (a) Does a frog
have a diaphragm? The diaphragm helps us to bring air in.(b) What acts like a diaphragm for the frog
to help bring air in?
Internal Structure
Skin
Heart
Lungs
Stomach
Esophagus
Large Intestines
Kidneys
Urinary Bladder
Comparison to Human
Body System