Download part 1—external anatomy

Name ________________________________________ Date _________________ Period ___________
FROG DISSECTION—Rana pipiens
PART 1—EXTERNAL ANATOMY
Follow these instructions carefully. Record the Description/comparison to humans and function on
the chart on page 3.
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.
2. Look at the large, protruding eyes. Explain why the position of the eyes is an advantage to the frog. Observe
the extra set of eyelids.
3. Notice that the frog has no neck. Explain how this might 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.
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. Record which jaw has
teeth. These teeth are called maxillary teeth. Notice that they slant inward. Explain how they would 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. Explain how these teeth would 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.
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. Look
at the human model of the ear and compare the frog’s Eustachian tube with the human. Record where the probe
goes.
9. Find the tongue. Look at where it is attached to the mouth. Explain how a frog uses 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.
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. This part compares to
the human epiglottis. Look at the diagram of the human respiratory system in your spiral.
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. The frog’s skin is similar to the earthworm in that oxygen and carbon dioxide is exchanged through the
skin. We have much thicker skin with a layer of fat under it (like the chicken skin).
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.
14. Locate the liver. It is right below and surrounding the heart. The liver has three lobes.
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.
16. Find the lungs. These are two thin-walled, reddish-brown sacs located below the heart and liver. Place an
eye dropper in the glottis (located in the mouth), squeeze the eye dropper. The frog’s lungs are much smaller in
relation to the body than human’s lungs.
17. Find the stomach. It is a curved, white structure. Cut open the stomach along the outside curve. See what
the frog had for its last meal.
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
19. See the small intestine, the main organ of digestion, leading from the other end of the stomach.
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 but only one in the frog.
21. 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.
22. The urinary bladder is a clear sac located below the kidneys.
23. 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.
24. 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?
FROG PART
HOW STRUCTURE
COMPARES TO HUMAN
FUNCTION FOR FROG
Nostril
(external)
Nostril
(internal)
Neck area
Teeth
(location & type)
Eye position
Eyelid
Ear
(tympanic membrane)
Glottis/Epiglottis
Tongue
(attachment)
Eustachian tube
Equalize pressure between
inner ear and outside air
Is your frog male or female? _____________________________________________________________
Structure
Skin
Heart
Liver
Gall Bladder
Lungs
Stomach
Comparison to Human
What Body System
Structure
Comparison to Human
What Body System
Esophagus
Small Intestines
Large Intestines
Kidneys
Urinary Bladder
Did your frog have ovaries or testes?_____________________ Description: _______________________
_____________________________________________________________________________________
What is the function of the fat bodies?______________________________________________________
Label the parts of the male frog