Frog External Anatomy – Harmony High School

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Frog External Anatomy
1. Observe the dorsal and ventral sides of the frog.
Dorsal side color ___________ Ventral side color

2. Examine the hind legs. How many toes are present on each
foot? ________
Are the toes webbed? ______

3. Examine the forelegs.
How many toes are present? _________Are the toes
webbed? _______

4. Use a ruler to measure your frog, measure from the tip of
the head to the end of the frog's backbone (do not include the
legs in your measurement). Compare the length of your frog to
other frogs

Your Frog (cm)              Frog 2               Frog 3          Frog 4      Frog 5

5. Locate the frog's eyes, the nictitating membrane is a clear membrane that attached to the bottom of the eye.
Use tweezers to carefully remove the nictitating membrane. You may also remove the eyeball.
What color is the nictitating membrane? _______
What color is the eyeball? _________

6. Just behind the eyes on the frog's head is a circular structure called the tympanic membrane. The tympanic
membrane is used for hearing. Measure the diameter (distance across the circle) of the tympanic membrane.
Diameter of tympanic membrane _______cm

7. Feel the frog's skin. Is it scaley or is it slimey? ____________

Anatomy of the Frog's Mouth

Procedure: Pry the frog's mouth open and use scissors to cut the angles of the frog's jaws open. Cut deeply
enough so that the frog's mouth opens wide enough to view the structures inside.

1. Locate the tongue. Play with the tongue. Does it attach to the front or the back of the mouth? __________
(You may remove the tongue)

2. In the center of the mouth, toward the back is a single round opening. This is the esophagus. This tube leads
to the stomach. Use a probe to poke into the esophagus.

3. Close to the angles of the jaw are two openings, one on each side. These are the Eustachian tubes. They are
used to equalize pressure in the inner ear while the frog is swimming.

Insert a probe into the Eustachian tube. To what structure does the Eustachian tube attach?
4. Just behind the tongue, and before you reach the esophagus is a slit like opening. (You may need to use
your probe to get it to open up). This slit is the glottis, and it is the opening to the lungs. The frog breathes and
vocalizes with the glottis.

5. The frog has two sets of teeth. The vomarine teeth are found on the roof of the mouth. The maxillary teeth
are found around the edge of the mouth. Both are used for holding prey, frogs swallow their meals whole and
do NOT chew.

6. On the roof of the mouth, you will find two tiny openings, if you put your probe into those openings, you will
find they exit on the outside of the frog. These are the nostrils.

Draw the frogs mouth. Label each of the structures underlined above.
         Complete the chart below

                Structure                           Function                                Location

      Vomarine teeth

      Eustachian tubes

      Nictitating Membrane

      Tympanic Membrane




Frog Internal Anatomy

Dissection Instructions
1. Place the frog in the dissecting pan ventral side up.

2. Use scissors to life the abdominal muscles away from the body cavity.
Cut along the midline of the body from the pelvic to the pectoral girdle.

3. Make transverse (horizontal) cuts near the arms and legs.

4. Life the flaps of the body wall and pin back.

*If your specimen is a female, the body may be filled with eggs and an
enlarged ovary. You may need to remove these eggs to view the organs.

Locate each of the organs below.
Fat Bodies --Spaghetti shaped structures that have a bright orange or yellow color, if you have a particularly fat
frog, these fat bodies may need to be removed to see the other structures. Usually they are located just on the
inside of the abdominal wall.
Peritoneum A spider web like membrane that covers many of the organs, you may have to carefully pick it off to
get a clear view
Liver--The largest structure of the the body cavity. This brown colored organ is composed of three parts, or lobes.
The right lobe, the left anterior lobe, and the left posterior lobe. The liver is not primarily an organ of digestion,
it does secrete a digestive juice called bile. Bile is needed for the proper digestion of fats.
Heart - at the top of the liver, the heart is a triangular structure. The left and right atrium can be found at the top
of the heart. A single ventricle located at the bottom of the heart. The large vessel extending out from the heart is
the conus arteriosis.
Lungs - Locate the lungs by looking underneath and behind the heart and liver. They are two spongy organs.

Gall bladder--Lift the lobes of the liver, there will be a small green sac under the liver. This is the gall bladder,
which stores bile. (hint: it kind of looks like a booger)
Stomach--Curving from underneath the liver is the stomach. The stomach is the first major site of chemical
digestion. Frogs swallow their meals whole. Follow the stomach to where it turns into the small intestine. The
pyloric sphincter valve regulates the exit of digested food from the stomach to the small intestine.
Small Intestine--Leading from the stomach. The first straight portion of the small intestine is called the
duodenum, the curled portion is the ileum. The ileum is held together by a membrane called the mesentery. Note
the blood vessels running through the mesentery, they will carry absorbed nutrients away from the intestine.
Absorption of digested nutrients occurs in the small intestine.
Large Intestine--As you follow the small intestine down, it will widen into the large intestine. The large intestine
is also known as the cloaca in the frog. The cloaca is the last stop before wastes, sperm, or urine exit the frog's
body. (The word "cloaca" means sewer)
Spleen--Return to the folds of the mesentery, this dark red spherical object serves as a holding area for blood.

Esophagus--Return to the stomach and follow it upward, where it gets smaller is the beginning of the esophagus.
The esophagus is the tube that leads from the frogs mouth to the stomach. Open the frogs mouth and find the
esophagus, poke your probe into it and see where it leads.

        STOP!     If you have not located each of the organs above, do not continue on to the
        next sections!

        Removal of the Stomach: Cut the stomach out of the frog and open it up. You may find what
        remains of the frog's last meal in there. Look at the texture of the stomach on the inside.

        What did you find in the stomach?

        Measuring the Small intestine: Remove the small intestine from the body cavity and carefully
        separate the mesentery from it. Stretch the small intestine out and measure it. Now
        measure your frog. Record the measurements below in centimeters.

        Frog length: _______ cm                              Intestine length ________ cm

      Urogenital System - The frog's reproductive and excretory system is combined into one system called
      the urogenital system. You will need to know the structures for both the male and female frog,
Kidneys - flattened bean shaped organs located at the lower back of the frog, near the spine. They are
often a dark color. The kidneys filter wastes from the blood.

Testes - in male frogs, these organs are located at the top of the kidneys, they are pale colored and

Oviducts - females do not have testes, though you may see a curly-q type structure around the outside of
the kidney, these are the oviducts. Oviducts are where eggs are produced. Males can have structures that
look similar, but serve no actual purpose. In males, they are called vestigial oviducts.

Bladder - An empty sac located at the lowest part of the body cavity. The bladder stores urine.

Cloaca - mentioned again as part of the urogenital system - urine, sperm and eggs exit here.

 Label the parts of the urogenital system below.
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