Laura Franks, 7Th Grade Science, Wilsonhigh School, Lauderdalecounty

Frog Dissection

Laura Franks, 7th Grade Science, WilsonHigh School, LauderdaleCounty

Title Screen

Script:

This is a dissecting pan.
Place a paper towel in the dissecting pan to absorb moisture from the frog.
These are dissecting tools that you will use: Dissecting pins, scalpel, dissecting scissors, forceps, and a dissecting needle. You will also use an apron, goggles, and gloves. Remember: goggles are NOT forehead protectors. Also, be sure to tell the teacher if you are allergic to latex.
Dissecting pins are used for pinning the specimen to the dissecting pan.
A scalpel is used to make an incision in the frog’s skin and muscle layer.
Dissecting scissors are used to cut through the sternum, and to cut through tougher tissue.
Forceps are used to remove parts of the specimen.
A dissecting needle is used to probe and point out specific parts of the specimen.
Be careful and use extra care when using dissecting tools. They are sharp and can be dangerous when misused. Remember to report accidents and injuries to your teacher!
Before making any incision, you should examine some external features of the frog. Place the frog “belly-down” so that you see the dorsal side of the frog. Use your dissecting needle to point to the frog’s eye. Frogs have special eyelids (nictitating membranes) that allow them to see underwater as well as on land.
Now, use your dissecting needle to point to the frog’s nares (nostrils). The frog’s nares allow them smell and breathe.
Now, find the tympanum. The tympanum is the external ear drum of the frog. It passes sound to the internal eardrum. The tympanum also amplifies croaking sounds.
Notice the hind legs of the frog. The webbed feet allow the frog to swim, and the powerful legs allow the frog to jump a distance twenty times the length of its body.
Now, point to the frog’s cloaca. The cloaca is the region where the legs come together. The cloaca is the area from which urine and feces are removed. Depending on the sex of the frog, sperm or eggs will also exit the cloaca.
The sex of a frog is difficult to determine, but a male frog usually has a larger tympanum. A male will also have a larger thumb. This larger thumb is used to grasp the female. Although the male frog will have larger typanums and thumbs, a female frog’s overall size is larger—especially when she is full of eggs. When dissecting the frog, if eggs are present, you know you have a female!! The eggs will resemble coffee grounds or potting soil.
This frog’s bladder has been displaced through the cloaca. The normal location should be inside the frog’s body. This displacement probably happened during the shipping process.
Now, turn the frog over to view the ventral side. The thoracic region is the chest area. The abdominal region is belly area.
Pin each leg of the frog to hold it steady to the dissecting pan. Now, you are ready to make your first incision.
Now, make a vertical incision in the abdominal region. Be careful to cut only the skin and muscle layer of the frog. Do not cut too deep because that may damage the organs.
Now, make a horizontal incision at the top and bottom of the abdominal area.
Peel back the skin and pin it down. You may also use scissors to cut through the muscle layer. Peel back the muscle layer and pin it down. If you have trouble keeping these sections pinned, you may use the scissors to remove the skin and muscle.
Use the dissecting scissors to make a vertical incision in the sternum. Pin back the skin and muscle layers of the thoracic region.
If your frog has eggs, remove them so that you have a better view of the internal organs.
Now, using your dissecting needle, see you if can identify the following parts:
The heart- near the center of the thoracic region
The lungs- on each side of the heart
The liver- large, dark organ of the abdominal region
The stomach- J shaped organ under the liver

Trace to the end of the stomach until you reach the…

The small intestine

Trace to the end of the small intestine until you reach the…

The large intestine
The bladder- transparent membrane near the cloaca
The kidneys- near the dorsal side of the frog on each side of the spinal column
Ovaries- resemble pasta noodles
Fat Bodies- banana shaped organs

Now that you have identified those organs, use your scissors and forceps to remove the organs and place them on the chart provided by your teacher.
After you complete the initial dissection of the frog, follow your teacher’s instructions for any further exploration.
Then, follow your teacher’s instructions for cleaning up!

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