Download External Anatomy

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Systems of the Frog
No two animal types have exactly the same internal organs. However, animals in the same phylum should have
organs that are somewhat similar. Frogs and humans are both chordates, and their internal organs, especially
those of the digestive system, are similar. Thus, if you study the structures of the frog systems, it will help you
better understand the structures of the human systems.
External Anatomy
Obtain a frog from your teacher and gently place it in the dissection tray.
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Observe the exterior of the frog. Describe the texture and color of the skin.
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Observe the location of the frog’s eyes relative to the head. Where are the eyes located on the frog? How
might this be an adaptation for its way of life?
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Right behind the eyes are darker circular structures called the tympanic membranes. What do you think is
their function?
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Observe the frog’s feet (in particular the toes). Compare the frog’s feet to that of humans. Develop a
hypothesis as to why the frog’s feet have the characteristics they do.
Digestive System
The Mouth
One can think of the digestive system as a long hollow tube extending through the body. This tube is open to
the outside at both ends. One opening is the mouth, while the other opening is the cloaca.
Examine the mouth of your frog. The mouth can be opened more easily by cutting the edges of the jaw with
scissors. See Figure 1 as a guide. You will have to cut through bone.
Compare the frog’s tongue to a human’s.
 How do the tip ends of the frog’s tongue differ from a human’s?
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How does the point of attachment of the tongue to the lower jaw differ?
Locate the slit-like glottis in the center of the back of the mouth.
 Where do you think the glottis leads?
Locate the esophagus.
 Where do you think the esophagus leads?
Rub your finger along the inside edge of the frog’s upper jaw. You should feel the maxillary teeth (it should
feel like sandpaper).
 Are any maxillary teeth also along the lower jaw edge?
Compare these teeth to human teeth.
 How do the structure of the maxillary teeth differ from the structure of human teeth?
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Do they have the same functions as human teeth?
Extending from the roof of the mouth are two vomerine teeth.
 What do you think is their function?(Hint: think how a frog eats from your prior knowledge)
Internal Organs
Place your frog on its back in the dissecting pan. Following Figure 2, use scissors to cut through the skin along
the dashed lines. Be careful not to cut into the organs! Point the scissors tips upward while cutting the skin.
Now follow the same procedure to cut through the muscle.
If your frog is female and contains black eggs, they must be carefully removed before other organs can be
observed.
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Put a probe through the glottis – where does it lead?
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Put a probe through the esophagus – where does it lead?
Locate the liver and gall bladder.
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How many lobes does the liver have?
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Describe the appearance and location of the gallbladder.
Locate the stomach
 Describe its shape and location.
Using scissors, remove the stomach from the inside of the frog. Once outside the frog, cut along the outer curve
of the stomach. Examine the contents of the stomach and it’s lining.
 Describe what the lining of the stomach looks like.
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Was there anything inside the stomach when it was cut open? Describe what you see.
The small intestine is surrounded by a thin membrane called the mesentery.
 What do you think is the function of the mesentery?
Remove the small intestine, carefully cut the mesentery, and carefully stretch the intestines out. Determine its
length.
 Length: _______ cm
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If the approximate length of the human small intestine is 30 ft (12 inches = 1 foot, 2.54 cm = 1 inch).
Approximately how many times longer is a human’s small intestine compared to a frog?
Locate the large intestine.
 To where does it lead?
Remove the large intestine and cut it open.
 Describe the contents of the large intestine.
Circulatory System
The Heart
Examine the heart lying in a thin sac, the pericardium. Use your probe to locate the great veins and arteries
leading to and from the heart. Examine the lungs and notice the pulmonary veins and pulmonary arteries
connecting the heart and lungs.
Remove the heart, leaving as much of the blood vessels attached as possible. Examine the front side. Locate
the right atrium, left atrium, and ventricle. The large vessel arising from the ventricle and forming a “Y” at the
top of the heart is the conus arteriosus.
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Make a sketch (below) of the heart, labeling the right and left atria, ventricle, and conus arteriosus.
The Urogenital System
Locate the cream colored oviducts through which eggs pass from the anterior of the body cavity to the posterior
opening, the cloaca. Remove the oviducts to reveal the brownish kidneys. The kidneys lie along the back of
either side of the spine. Notice they are covered by a thin, tough membrane, the peritoneum, which lines the
body cavity. Locate a small twisting tube, the ureter, leading from each kidney to the cloaca. Attached to the
cloaca is the urinary bladder.
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What is the function of the urinary bladder?
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What is the function of the kidneys?
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Make noteworthy observations of the following:
Oviducts (female only) * if you have a male frog, you need to find a group that has a female frog so that you can answer this
Kidneys
Respiratory System
The Lungs
Locate the lungs situated near the heart. Make noteworthy observations of the exterior of them. Now remove
one lung and neatly slice it in half to expose the interior surface. Make noteworthy observations of the interior.
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Lung Observations:
Exterior
Interior