Name _______________________________ Period ______ Date ____________________
Frog Dissection Lab
Highlight the main points (5pts)
Background: Frogs are small animals belonging to a group called vertebrates (animals with
backbones) known as amphibians. They live part of their life in water and the other part of it
on land. Amphibians are cold blooded animals. Their skin absorbs water into their body so
they do not have to drink water to survive. Frogs have strong hind legs to enable them to leap
forward at great distances. The front legs are short. They are used to prop the frog up when
its sits. The largest frog is the giant Goliath frog of West Central Africa. It can grow up to more
than 30 centimeters. The largest frog in our country is the bullfrog and it can grow up to more
than 5 inches long. The smallest frog found so far is the size of a pea in Southeast Asian
island of Borneo. Frogs are special; they can breathe by means of the lungs and also through
their skin. Frogs are important to humans. They are also a source of food in some countries.
They eat pests and are a big part of the food chains. We use them in medical research and for
dissection in schools to learn about their anatomy.
Purpose: To be able to learn the external and internal parts of a frog. To investigate the
different body systems and to learn about proper dissecting techniques.
Materials: leopard frogs (Rana pipiens), frog dissection guide, scissors, dissecting tray, probe,
forceps, dissecting teasing needle, dissecting pins, map pencils and clean up supplies.
Procedure: Part 1: External Anatomy
1. Obtain a dissecting tray, a frog and a set of dissecting instruments.
2. Lay the frog dorsal surface up in the dissecting tray.
3. Notice the thinness of the frog’s skin. Note the absence of scales, hair, or any other
protective covering. Begin with the questions.
PART I:
Questions and Drawings:
1. Draw a section of skin in the circle below. Make a colored detailed drawing. Label skin.
(4 pts.)
_________________
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2. Measure your frog. Measure in centimeters. (2pts.)
a. Length
_____ cm
b. Width
_____ cm
(Measure from the tip of the head
(Measure at the widest part)
to the hind legs)
3. Describe the frog’s skin. Be specific. (2 pts.)
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4. Locate the external nares, which are also called the nostrils. How many are there and
what do they look like? (2 pts.)
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5. The eyes are easy to find. Examine each eye closely and locate the nictitating
membrane, a third eyelid. In a living frog, the nictitating membranes are transparent
and cover the eyes when the frog is underwater. Why is this structure beneficial to the
frog? (2 pts.)
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Procedure:
Locate the shoulder joints, elbow joints, and wrist joints of the forelimbs. Count the digits on
each forelimb. The innermost digit of male frogs has a swollen pad during the breeding
season.
6. Near the end of the body is the opening of the cloaca. Feces, urine, and reproductive
cells are expelled through the cloaca. How is this different from the human? (2 pts.)
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7. Examine the muscular hind limbs. Locate the hip joints, knee joint, and ankle joints.
Examine the webs of each foot. Count the digits on each hind limb. (2 pts.) How many
are there?
___________ X 2 = ___________
Questions and Drawings:
8. How many digits are on the front legs and hind legs? (2 pts.)
Front Legs ______
Hind Legs ______
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9. Draw a forelimb and hind leg in the space below. Make sure you draw a detailed
drawing. Color the leg as it appears. Label the left circle forelimb and right hind leg.
(4 pts. each – 8 total)
___________________________
___________________________
10. Gently pry the mouth open and use scissors to cut the jaws at the joints. Examine the
inside of the mouth. Refer to the Frog Dissection Guide at your lab station for help.
Find two bony knob-like bumps projecting from the upper surface of the mouth. These
are the vomerine teeth. If you rub your finger along the inside of the jaw, you will feel
the maxillary teeth. What is the difference between the vomerine teeth and maxillary
teeth? (2 pts.)
__________________________________________________________________
__________________________________________________________________
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11. Find the tongue. What do you notice about it that is unusual? Draw and describe the
tongue, its shape and color below. Label tongue. (4 pts.)
Describe the tongue
________________________
________________________
________________________
________________________
_____________________
12. Directly behind the tongue, locate a raised structure with a slit in it. This is called the
glottis, the opening of the air passageway that leads from the mouth to the lungs.
Behind the glottis is the opening of the esophagus. Draw and label the tongue,
vomerine teeth, and maxillary teeth. Include the vocal sacs if you have a male frog.
Label inside of frog mouth below. (4 pts.)
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____________________
13. The openings of the Eustachian tubes are located near the corners of the mouth. Insert
a dissecting needle into one opening and push carefully. Observe where the needle
comes out. What do you notice? (2 pts.)
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14. Two large, muscular pads are found in the roof of the mouth. The frog retracts its eyes
into these pads when it blinks. Why is this good? (2 pts.)
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Frog Diagrams
Directions: Label and COLOR the following diagram. (Eye, tongue, nares or nostrils,
maxillary teeth, vomerine teeth, glottis, tympanum, Eustachian tubes, and esophagus.)
(9 points total)
Frog Mouth
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For the diagram below, label, COLOR the following parts: eye, tympanum, digits on the
forelegs and hind legs, and cloaca.
External Anatomy of the Frog
Part II:
STOP! Internal Dissection tomorrow…
Clean up your lab station. Wipe down the table with cleaner and paper towels. Make
sure to put your specimen in a baggie that the teacher will provide for you. Don’t start
the internal dissection until tomorrow.
Procedure: Part 2 Internal Anatomy
15. Lay the frog ventral (stomach) surface side up on the dissection tray. With forceps, lift
the skin over the frog’s abdomen, insert the point of a pair of scissors, and make the
cuts shown in the Frog Dissection Guide at your lab station. With forceps, lift the skin
over the frog’s abdomen, inset the point of a pair of scissors, and make the cuts. After
cutting, lift one corner of the skin with forceps and use the scissors to separate the skin
from the underlying muscles. Completely cut away the skin from the abdomen and
throat.
16. With forceps or probe lift and make an incision through the muscles of the abdomen.
Use the point of a pair of scissors to make the cuts shown in the Frog Dissection
Guide at your lab station. It will be necessary to cut the bones of the pectoral girdle
with scissors. Make the cuts carefully to avoid damaging the internal organs.
17. Cut off the body wall flaps of skin. This will expose the internal organs.
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18. If your frog is a female, the oviduct may be enlarged with eggs and may partially cover
the digestive organs. If this is the case, carefully cut away the oviduct and remove
enough of the eggs to clearly see the internal organs.
19. At the anterior of the abdominal cavity is the liver, a large, brown gland of three lobes.
Lift the lobes of the liver and search for a dark, greenish sac. This sac is called the gall
bladder. The green color results from a pigment in the bile. Bile is a secretion of the
liver that is stored in the gall bladder. Draw the liver below. Color the liver as it appears.
Label liver below. (4 pts.)
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20. Describe the shape and size of the liver. (2 pts.)
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21. The J-shaped, muscular sac partially beneath the liver on the left side of the frog’s body
is the stomach (left and right refer to the frog’s left and right – anatomical). The lower
end of the stomach attaches to the small intestine. Two divisions make up the small
intestine: the duodenum is the less folded portion that attaches to the lower end of the
stomach and the ileum is the highly folded portion. The small intestine and the other
internal organs are held in place by membranes called the mesenteries. Notice that the
digestive organs are attached to numerous blood vessels. Draw the stomach below.
Make sure to color it as it appears. Label stomach below. (4 pts.)
_________________
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22. Open up the stomach. Look inside. What do you see? If you find anything interesting
make sure to let the teacher know. If you find nothing state why it is empty. (2 pts.)
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23. Now look for the small intestines. They are beige colored small tubes held up by a thin
skin called the mesentery. Draw and label the small intestines and mesentery below.
Color these organs as they appear. (4 pts.)
______________________
24. Look between the stomach and the duodenum to find the pancreas, a long and thin
mass of tissue in the mesentery between the two organs. Lift the ileum and find the
spleen, a somewhat round organ that is brown in color. The spleen is actually part of
the circulatory system. Follow the ileum until it runs into a much wider part of the
digestive tract, the large intestine. Refer to the Frog Dissection Guide or your textbook
for the function of each of the organs below. (6 pts. total)
Structure
System and its Function
Liver
Gall Bladder
Stomach
Pancreas
Small Intestine
Large Intestine
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Shape and Color
25. The heart is located just anterior to the liver. A touch membrane called the pericardium
covers the heart. Lift the pericardium with forceps and begin cutting it away. The large,
lower chamber of the heart is the ventricle. Draw the heart and label the different
chambers and heart below. Remember the frog has 2 atria and 1 ventricle. Color this
drawing as it appears. (4 pts.)
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Cut the digestive organs out of your frog. Against the back wall are the two flattened,
oblong kidneys. If your frog is female, the ovaries might be filled with eggs. If so, remove
them. Attached just anterior to each kidney is a structure with long, finger-like projections.
These are the fat bodies. The fat bodies are usually yellow or a beige color. Draw a set of
fat bodies in the space below. Color as they appear. Label fat bodies. If you have a male
frog you get to draw a picture on the right side. If your frog is male an oval testis is
attached ventrally to each kidney by a membrane. It may be possible to see small tubes
called the vasa efferentia, in the membrane. A ridge along the ventral surface of the kidney
is the adrenal gland. Beside the kidney is a long coiled tube called the oviduct. The
oviduct is vestigial in the male. The lower end of the oviduct s expanded and is called an
ovisac. The ovisac attaches to the urinary bladder. Lift the urinary bladder and gently pull
away the membrane between it and the kidney. You may be able to find the ureter, a
colorless tube that drains urine from the kidney to the urinary bladder. Draw the 2 kidneys
and spinal cord in the space below. Color it as it appears. Refer to the Frog Dissection
Guide for help. The fat bodies on the left and kidneys on the right circle.
(4 pts. each – 8 total)
_________________
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Summary: Write about amphibians and what you have learned about frogs. Include
information about this group of animals and their specific parts both internal and external.
Write a minimum of six complete sentences. (12pts.)
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Label any 6 parts of the frog. (6 pts.)
Internal Anatomy of the Frog
Label only 6 below.
A - ________________________
B - ________________________
C - ________________________
D - ________________________
E - ________________________
F - ________________________
G - ________________________
H - ________________________
I- ___________________________
J - __________________________
K - __________________________
L - __________________________
M - __________________________
N - __________________________
NO “O”
P - __________________________
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