Biology
Zoology Lab #15 – Frog Dissection
De Stigter
Name_____________
Period ____________
40
Introduction: The study of the frog has been a part of the curriculum in biology classes for many
years. These common, cold blooded organisms have been examined and dissected by more high
school and college students than any other organism. Many of the structures, organs, and systems
of the frog are similar to those of man, who is also a vertebrate. At the same time, the frog, an
amphibian, is quite different from man. Similarities and differences will be pointed out and noted
during this dissection.
External Dissection:
1. Place the frog on its ventral side and locate the anterior and posterior ends.
2. On the outside of the frog’s head are two external nares, or nostrils; two tympani which
act as eardrums, and two eyes which has three lids. The clear transparent lid covering the
eye is called the nictitating membrane.
3. Next flip the frog onto its dorsal side. Notice the difference of color between the dorsal
side of the frog and the ventral side. Why do you think they have this distinct coloration
difference?
4. In order to determine the sex of your frog take a look at the thumb pads of your frog’s
hand. A male typically has larger pads by its thumb than a female. Another way to
determine the sex of your frog is to compare its size to another frog. Females tend to be
larger than males in terms of their body size. Finally, the tympanum of a male is much
larger than that of a female frog.
5. Use dissecting pins to secure the frogs legs down to the tray. Using a scissors or razor
blade, cut the hinges of the mouth and open it wide. Locate the following structures found
inside of the mouth: vomerine teeth, maxillary teeth, internal nares, tongue, esophagus,
glottis, and the Eustachian tubes (small holes located towards the roof of the mouth that
lead to the tympanum; used to equalize pressure, similar to swallowing in humans).
Internal Dissection: Muscular System
1. In order to look at the internal contents and structures of your frog, it has to be skinned.
Look at the back of your lab guide and follow the instructions for “Skinning the Frog”.
Remember to keep your cuts superficial!!!
2. Starting at the posterior end of the frog, locate the gastrocnemius. Use your needle to
find the Achilles tendon which runs from the posterior end of the gastrocnemius past the
ankle joint.
3. Move anterior and locate the triceps femoris. Then look at the rest of the muscles that
make up the thigh region. The number of muscles explains why frogs have such a great
leaping ability.
4. Moving anterior, locate the rectus abdominus. You should clearly be able to see six
distinct muscle areas. Notice the linea alba which is a line of tissue that splits the rectus
abdominus in half.
5. Moving lateral from the rectus abdominus is the pectoralis muscle. It runs from the
posterior area of the rectus abdominus anterior towards the head of the frog.
Internal Dissection: Digestive System
6. Next take a scissors and cut through the muscles and the sternum to open up the body
cavity. If your frog is a female, the abdomen may be filled with many dark colored eggs. If
so, remove the eggs from your specimen and dispose of them in the garbage can.
7. Use the diagram below or the dissection manual provided to help identify the organs of
the digestive system: esophagus, stomach, small intestine, large intestine, cloaca, liver,
gall bladder, and pancreas.
Internal Dissection: Circulatory System
8. Next locate the different structures of the circulatory and respiratory systems in the chest
cavity. Locate the 3 chambered heart which is anterior to the liver. Notice the right and
left atria as well as the ventricle. Feel the consistency of the different chambers. Which
one is more muscular? Why?
9. Next locate the truncus arteriosius which is the main artery branching off of the
ventricle. Notice how it branches off into two separate arteries. The artery that carries
deoxygenated blood to the lungs is called the pulmocutaneous arch. The one that
carries oxygenated blood to the rest of the body is called the truncus arteriosius.
10. Two of the large veins that carry deoxygenated blood from the body back to the heart are
called the ventral abdominal vein and the anterior vena cava. The ventral abdominal
vein can be found running anteriorly along the ventral midline. This vein carries blood
to the heart from the legs and pelvic regions. The anterior vena cava is the largest vein
because it takes all blood coming from the body and sends it into the right atria.
11. Finally, find the lungs of the frog. They should be red/brown in color and located
anterior of the stomach.
Internal Dissection: Urinary and Reproductive Systems
12. Next remove the intestines and liver. Use the diagram below to identify the parts of the
urinary and reproductive systems. Remove the peritoneal membrane, which is
connective tissue that lies on top of the red kidneys. Observe the yellow fat bodies that
are attached to the kidneys. Find the ureters, urinary bladder, testes and sperm ducts
in a male. Find the ovaries, oviducts, and uterus in a female.
Internal Dissection: Skeletal System
13. Next carefully remove all tissues and organs of the frog. Make sure to dispose of
everything in the trashcan.
14. To end the dissection, find the following bones in the skeletal system of the frog: skull,
humerus, radio-ulna, carpals, metacarpals, phalanges, vertebrae, scapula, ilium,
ischium, urostyle, femur, tibio-fibula, tarsals, and metatarsals. Note how all of the
bones work together for a frog. Especially look at the joints of the frog. Notice how
ligaments connect bone to bone and hold bones together.
***Clean up your lab dissection area. Throw all frog contents into the garbage can. Clean your lab
equipment and wipe off your table with the blue cleaning spray. Finally go and wash your hands in
the bathroom.***
Biology
Zoology Lab #15 – Frog Dissection Report
De Stigter
Name_____________
Period ____________
1. What do you think the function of the nictitating membrane is, and why?
2. A frog does not chew its food. What do the positions of its teeth suggest about how the frog
uses them?
3. Using words, trace the path of the food through the digestive tract.
4. Using words, trace the path of blood through the circulatory system starting at the right
atrium.
5. The abdominal cavity of a frog at the end of hibernation season would contain very small fat
bodies or none at all. What is the function of the fat bodies?
6. The frog’s legs are very muscular compared to the rest of its body. Explain why their
powerful legs are useful for both land and water.
7. The skeletal system and the muscular system work hand in hand to aid in the movement of a
frog. Explain what muscles and bones a frog uses as a defense mechanism when it jumps
away from predators.
Label the Diagram:
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B__________________
C__________________
D__________________
E__________________
F__________________
G__________________
H__________________
I___________________
J___________________
K__________________
L__________________
M__________________