Name _______________________________________________
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.

Observe the exterior of the frog. Describe the texture and color of the skin.
Skin is smooth moist and dark green to brownish with black spots. Ventral side (bottom of frog is light in color
yellowish white)

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?
Eyes are far forward on the head and stick up above the skull and mouth. Avoid predators by staying under
water, but able to still see clearly above the waterline, hunt for prey using the same technique.

Right behind the eyes are darker circular structures called the tympanic membranes. What do you think is
their function?
These are the frogs eardrums – used for hearing.

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.
Frog feet seem to be comprised of cartilage, muscle and bone. Between from “toes” there are large flaps of skin
(webbing). Foot is very large in relation to rest of body and matches the large leg size. Frogs have
overdeveloped legs and webbed feet for jumping away from danger and for swimming efficiently under water.
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?
The tip of the tongue is broader and has a fork shape.

How does the point of attachment of the tongue to the lower jaw differ?
The tongue attaches at the front of the mouth, whereas in a human the tongue attaches at the rear of the mouth.
Therefore the frogs tongue flips forward and is hinged in the front.
Locate the slit-like glottis in the center of the back of the mouth.
 Where do you think the glottis leads?
The glottis is the opening to the airway for the frog and leads to the lungs
Locate the esophagus.
 Where do you think the esophagus leads?
Located behind the glottis - To the stomach
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?
No, maxillary teeth cannot be felt.
Compare these teeth to human teeth.
 How do the structure of the maxillary teeth differ from the structure of human teeth?
Maxillary teeth are extremely small and seem to be all the same size and possibly the same shape. Human teeth
are shaped differently depending upon function.

Do they have the same functions as human teeth?
No, human teeth have evolved to eat a wider variety of foods than frogs there for teeth have been shaped to suit
certain functions (grinding, tearing, cutting). Frogs are not chewing their food, but more often swallowing it
whole.
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)
Vomerine teeth are slightly hooked and allow the frog to keep a grip on its prey and prevent the prey from
escaping from it’s mouth.
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.
 Put a probe through the glottis – where does it lead?
Goes to the lungs.
 Put a probe through the esophagus – where does it lead?
Goes to the stomach
Locate the liver and gall bladder.

How many lobes does the liver have?
3 lobes
 Describe the appearance and location of the gallbladder.
The gallbladder looks like a partially deflated balloon attached to the under
side of the liver. It is whitish to slightly dark green in color.
Locate the stomach
 Describe its shape and location.
The stomach is a “J” shaped pouch and is located mostly under the liver.
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.
The lining of the stomach has folds of tissue that form ridges along the interior. A cross section looks like a star
and has radial symmetry. Folds increase the surface are of the stomach for mechanical (mixing) digestion and
absorption of nutrients.

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?
This membrane attaches to the intestines and holds them in place by attaching them to the rear wall of the
abdominal cavity, you have the same structure in your abdominal cavity.
Remove the small intestine, carefully cut the mesentery, and carefully stretch the intestines out. Determine its
length.
 Length: _6-10______ cm

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?
Human intestine is about 914 cm. About 90 times longer.
Locate the large intestine.
 To where does it lead?
Large intestine leads to the cloaca.
Remove the large intestine and cut it open.
 Describe the contents of the large intestine.
Brownish green soft material, moist, that appears to be feces.
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.

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.

What is the function of the urinary bladder?
Holds urine generated by kidneys. Connects to cloaca where urine exits the body.

What is the function of the kidneys?
Filter nitrogen containing waste from the blood and maintains a steady pH within the blood.

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
Small whitish yellow tubes that resemble noodles located under the fat bodies near the dorsal side of the
frog.
Kidneys
Bean shaped purplish red organ (2) located on either side of the spine. Each has blood vessels that enter from
frog’s circulatory system. Peritoneum (clear membrane) can be seen around the 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.

Lung Observations:
Exterior
Lungs are purplish red and are located under liver on either side of the chest. Red blood vessels can be
observed on the outside of each lung. Lungs are small approximately the size of two pencil erasers end to end.
Interior