Frog External Anatomy · (group names, period, frog’s name) Frog External Anatomy 5. During breeding season, the base of a male frog’s thumb becomes thickened to form a little

Biology – Frog dissection lab Thursday May 17, 2012

Perry High School

Mr. Pomerantz_______________________________________________________________________________Page 1 of 7

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Review:

Dorsal = top side (back) Anterior = toward the head (front end)

Ventral = underside (belly) Posterior = toward the tail (rear end) Lateral = sides

1. Obtain a frog and rinse off.

2. Obtain dissection tools (paper for labeling, scissors, scalpel, forceps, tray, pins, probe, scissors,

gloves (optional))

3. Place your frog on a dissection tray.

4. Obtain a plastic bag and write the following information

(group names, period, frog’s name)

Frog External Anatomy

5. During breeding season, the base of a male frog’s thumb becomes thickened to form a little pad

called a nuptial pad (see figure 1).

• Do you think your frog is a male or female? ____________

6. Observe the dorsal and ventral sides of the frog.

• Dorsal side color ___________ Ventral side color ____________

• Why do you think the frog looks different on each side? Think about adaptations to its

surroundings. _____________________________________

__________________________________________________________________

_________________________________________________________________.

7. Examine the hind (posterior)

• How many toes are present on each foot? _______________

• Are the toes webbed? ___________

8. Examine the forelegs (anterior)

• How many toes are present? _________

• Are the toes webbed? _______

9. Use figure 2:

• Locate the frog's eyes. You will notice a clear membrane that attaches to the bottom of the

eye. This is called the nictating membrane. This membrane helps keep the eye surface

moist and functions like goggles to protect the eyes under water.

• Just behind the eyes on the frog's head is a circular structure called the tympanic

membrane. The tympanic membrane is used for hearing.

• Locate the external nostrils. The small pair of openings near the tip of the nose allows air to

enter or leave the mouth.

• Pin each underlined feature above and wait for the instructor’s approval before moving on.

Make sure all boxes above are initialed by your instructor before moving on.


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Begin Dissection

Inside Mouth Use Figure 2:

Pry the frog's mouth open and use scissors to cut the angles of the frog's jaws open where the arrows

indicate. Cut deeply enough so that the frog's mouth opens wide enough to view the structures

inside.

10. Back to front- a frog's tongue is fastened in the front, not the back and is folded backward to the

throat. The tongue of a frog is about a third of the frog's length. Sounds impressive, until you realize

if a human had a comparable tongue, it would reach a bellybutton. The tongue can flip back in

15/100 of a second. Locate the tongue.

11. 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 locate the esophagus.

12. The frog has two sets of teeth. The vomerine 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. Locate the vomerine teeth in the roof of the mouth and the

maxillary teeth along the upper jaw.

13. Locate the eye pouches inside the roof of the mouth. With your finger, firmly press on the top of

the eyes to see the eyes lower. If the eyes are already lowered, firmly push on them from the inside

of the mouth in order to make them rise. These pouches give the eyes added protection and when

the eyes are lowered they help to hold the food and push it toward the back of the throat.

14. Pin each underlined feature above and wait for the instructor’s approval before moving on

Internal Structures Use Figure 3:

Remove Outer Skin and muscle layer as shown in Figure 3: use scissors to lift the abdominal

muscles away from the body cavity (BE CAREFUL not to cut TOO DEEP and puncture

organs). Lift the outer flaps and pin back (DO not cut them off). You will need to cut the outer

flaps horizontally and vertically as shown.

*** If your frog is female, the body may be filled with eggs and an enlarged ovary. You may need to

remove these eggs to view the organs.***




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Use Figure 4 to locate the structures below:

15. 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. The amount of fat bodies tells you the

recent eating habits of the frog. Fat serves as a fuel reserve in times of low food intake (ex:

hibernation)

16. Liver--The largest structure of 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, however it does secrete a digestive juice called bile. Bile is needed

for the proper digestion of fats.

17. Gall bladder--Lift the lobes of the liver and locate a small green sac under the liver. This is the

gall bladder. The function of the gall bladder is to store bile.

18. 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.

19. 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.


21. 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

22. 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 (klo A’ kuh) in the frog. The cloaca is the last stop

before wastes, sperm, or urine exit the frog's body. (The word "cloaca" means sewer)

23. Spleen--Return to the folds of the mesentery, this dark red spherical object serves as a holding area

for blood



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Use Figure 5 to locate the structures below:

24. 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.

25. Lungs - Locate the lungs by looking underneath and behind the heart and liver. They are two spongy

organs


Excretory and Reproductive System

27. 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.

• Place a portion of the stomach under a microscope to observe the contents.

28. Measuring the Small intestine:

• Remove the small intestine from the body cavity and carefully separate the mesentery(web

like material) 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

Use Figure 6 (male) or 7(female) to locate the structures below

29. 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.



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30. Find the following structures according to the sex of your frog:

If your frog is

male:

If your frog is

female: Testes- in male frogs, these

organs are located at the top

of the kidneys, they are pale

colored and roundish.

Oviducts – Look for a

curly-q type structure

around the outside of the

kidney, these are the

oviducts. Oviducts are

where eggs are produced.

Both Ureters- Small tubes the carry urine from the kidney to the cloaca.

Bladder (use figure 4)- Once the kidneys have filtered the blood and sent the urine to the

cloaca, it is either eliminated immediately or stored in the urinary bladder. When empty

the frog’s urinary bladder looks lie a floppy clear bag.

Cloaca - urine, sperm and eggs exit here.

Figure 1

Clean Up • Place your frog and its removed parts in the bag. Seal bag and place in trash.

• Clean and return all dissecting equipment

• Clean all slides used for microscopes

• Clean up your work area and wash your hands. Make sure paper towels go into the trash

not recycling ☺

• Turn this lab in.



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Figure 2


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Documents

Frog External Anatomy · (group names, period, frog’s name) Frog External Anatomy 5. During breeding season, the base of a male frog’s thumb becomes thickened to form a little