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FROG DISSECTION LAB
EXTERNAL ANATOMY
- Observe the dorsal and ventral sides of the frog. Dorsal side color ___________ Ventral side color____________
- Examine the hind legs. How many toes are present on each foot? ________ Are the toes webbed? ______
- Examine the forelegs. How many toes are present? _________Are the toes webbed? _______ Male or female? (Hint: check thumb pad) _____
- Use a ruler to measure your frog, measure from the tip of the head to the end of the frog's backbone (do not include the legs in your measurement). Compare the length of your frog to other frogs
Your Frog (cm) Frog 2 Frog 3 Frog 4 Frog (^5) Average
L e n g th
- Locate the frog's eyes, the nictitating membrane is a clear membrane that is attached to the bottom of the eye. Use tweezers to carefully remove the nictitating membrane. You may also remove the eyeball. What color is the nictitating membrane? _______ What color is the eyeball? _________
- Just behind the eyes on the frog's head is a circular structure called the tympanic membrane. The tympanic membrane is used for hearing. Measure the diameter (distance across the circle) of the tympanic membrane. Diameter of tympanic membrane _______cm
- Feel the frog's skin. Is it scaly or is it slimy? ____________
Anatomy of the Frog's Mouth
Procedure: Pry the frog's mouth open and use scissors to cut the angles of the frog's jaws open. Cut deeply enough so that the frog's mouth opens wide enough to view the structures inside.
- Locate the tongue. Play with the tongue. Does it attach to the front or the back of the mouth? __________ (You may remove the tongue)
- 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 poke into the esophagus.
- Close to the angles of the jaw are two openings, one on each side. These are the Eustachian tubes. They are used to equalize pressure in the inner ear while the frog is swimming.
Insert a probe into the Eustachian tube. To what structure does the Eustachian tube attach?
- Just behind the tongue, and before you reach the esophagus, is a slit like opening. (You may need to use your probe to get it to open up). This slit is the glottis, and it is the opening to the lungs. The frog breathes and vocalizes with the glottis.
- 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.
- On the roof of the mouth, you will find two tiny openings. If you put your probe into those openings, you will find they exit on the outside of the frog. These are the nostrils, or nares.
On the diagram below, label each of the structures underlined above.
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.
Lungs - Locate the lungs by looking underneath and behind the heart and liver. They are two spongy organs.
Gall bladder --Lift the lobes of the liver, there will be a small green sac under the liver. This is the gall bladder, which+h stores bile. (hint: it kind of looks like a booger )
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.
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.
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 in the frog. The cloaca is the last stop before wastes, sperm, or urine exit the frog's body. (The word "cloaca" means sewer)
Spleen --Return to the folds of the mesentery, this dark red spherical object serves as a holding area for blood.
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.
STOP! If you have not located each of the organs above, do not continue on to the
next sections!
- 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. Look at the texture of the stomach on the inside.
- What did you find in the stomach?
- Measuring the small intestine: Remove the small intestine from the body cavity and carefully separate the mesentery 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
Urogenital System - The frog's reproductive and excretory system is combined into one system
called the urogenital system. You will need to know the structures for both the male and female frog,
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.
Testes - in male frogs, these organs are located at the top of the kidneys, they are pale colored and roundish.
Oviducts - females do not have testes, though you may see a curly-q type structure around the outside of the kidney, these are the oviducts. Oviducts are where eggs are produced. Males can have structures that look similar, but serve no actual purpose. In males, they are called vestigial oviducts.
Bladder - An empty sac located at the lowest part of the body cavity. The bladder stores urine.
Cloaca - mentioned again as part of the urogenital system - urine, sperm and eggs exit here.
Label the parts of the urogenital system below.
Study and Removal of the Frog's Brain
Starting at the most anterior part of the head, the olfactory nerves connect to the nostrils and
then to the olfactory lobes (A) where odors are processed. Just posterior to the olfactory lobes are two elongate bodies with rounded bases, this is the cerebrum (B), and it is the frog's thinking center. The cerebrum is the part of the brain that helps the frog respond to its environment. Posterior to the cerebrum are the optic lobes (C), which function in vision. The ridge just behind the optic lobes is the cerebellum (D), it is used to coordinate the frog's muscles and maintain balance. Posterior to the cerebellum is the medulla oblongata (E) which connects the brain to the spinal cord (F).
Brain Part
Cerebellum
Cerebrum
Olfactory Lobe
Optic Lobe
Function Letter
Complete the chart.
Medulla Oblongata
Removal of the Frog's Brain
Turn the frog dorsal side up. Cut away the skin and flesh on the head from the nose to the base of the skull. With a scalpel, scrape the top of the skull until the bone is thin and flexible. Be sure to scrape AWAY from you. With your scalpel held almost horizontally, carefully chip away the roof of the skull to expose the brain. Use scissors to cut away the heavier bone along the sides of the brain.
FROG BONES
The bones of the frog follow the same pattern (basically) as other vertebrates. The lower leg of the frog is a muscular leg that the frog uses for jumping. There are 3 main sets of bones in the lower leg. The femur is found in the upper thigh, and the tibiofibula is found in the lower part of the leg. The foot and ankle are made of the tarsals and metatarsals (toes). To expose the frog's leg bones you must remove the thigh muscle - the biceps femorus and the calf muscle - the gastrocnemius. You can leave the Achilles tendon intact (this tendon connects the muscle to the bone). The tarsals and metatarsals do not need to be exposed.
Clean your bones by removing the surrounding muscle. Bring the two bones on a paper towel. Good Luck!
Label the leg bones: Femur, Tibiofibula, tarsals, metatarsals, pelvic girdle
