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1. Put on an apron

2. Lay the frog in your dissecting tray with its ventral surface up and the head pointed away from you. Study Figure 33A-1 which shows the incisions you will make in the frog.

3. With forceps, lift the skin on the ventral surface of the frog near the hind legs. Insert the tip of your scissors through the skin where the hind legs meet.

4. Cut through the skin up the midline of the frog to the tip of the jaw.

5. Cut the skin laterally, just below the front legs and just above the hind legs as shown in Figure 33A-1. With your fingers, gently separate the skin from the underlying muscle tissue. Pull the flaps of skin as far as possible to the sides of the frog.

6. Using forceps lift the muscle layer on the ventral surface of the frog near the hind legs. With scissors, cut through the muscle layer, following the same incision pattern you used for the skin. When you reach the point between the front legs, you will be cutting through a bone that protects the heart. Be sure to keep the tips of your scissors tilted upward to prevent damaging the organs below.

7. When you have finished making your incisions, carefully pull the flaps of muscle to the sides.

8. Observe the organs as they are positioned in the body cavity. If you have a female frog, the body cavity may be filled with tiny black and white eggs. With forceps, remove the eggs and place them on a paper towel.



9. At the anterior end of the frog, find the large, greenish-brown liver. Lift the lobes of the liver to locate the  pea-shaped gall bladder. With scissors, carefully remove these organs.

10. Locate the heart, a triangular-shaped organ lying between the forelimbs at the anterior end of the frog.

11. Surrounding the heart, you will notice a thin membrane called the pericardium. With a scissors and a probe, cut the pericardium away from the heart. Do not cut through the blood vessels joining the heart.

12. Study the heart. Find the atria, the dark-brown structures, which make up the upper portion of the heart. Beneath the atria, observe the light-brown, cone-shaped ventricle.

13. With your probe, gently press on one of the atria and then on the ventricle. Note the muscularity of their walls.

14. On the ventral surface of the heart near the top, scrape away soft tissue until you locate a Y-shaped artery that connects with the ventricle.

15. This artery called the conus arteriosus, branches and forms two arches above the heart, which reunite below the heart to form the dorsal aorta.

16. Try to locate the major blood vessels in the frog.

17. Locate the lungs, two small, black, saclike structures on either side of the frog's heart.

18. Insert the tip of an empty medicine dropper into the glottis in the frog's mouth. Squeeze the bulb and observe what happens to the lungs.

19. Locate the large, muscular stomach. Follow the stomach anteriorly to find the short esophagus.

20. Follow the stomach posterior to find the narrow, tube like small intestine.

21. The tissues that hold the organs together and in place are called "Mesenteries". Find the light-brown pancreas, which is held in the mesentery between the stomach and the intestine.

22. In the mesentery near the stomach, also find a brown, bean-shaped organ called the spleen. The spleen produces red blood cells and filters out old blood cells.  

23. Find the yellow, flame-shaped, fat bodies. Notice where these structures are attached.

24. Trace the small intestine to the point where it becomes a wider tube. This is the large intestine. Compare the lengths and diameters of the small and large intestines.

25. The large intestine leads to the cloaca, the slightly enlarged portion of the digestive tract, which is just anterior to the cloacal opening or anus.

26. Remove the digestive tract by cutting through the anterior end of the esophagus and the posterior end of the large intestine. With your fingers, carefully tear away the mesentery to free the digestive organs. Stretch out the digestive tract. Notice that it is actually just one long tube.

27. With your fingers, press on the stomach and note how it feels. With scissors, make an incision along the outer curve of the stomach. Spread the stomach walls apart. Study the contents of the stomach. Observe the texture of the stomach lining.

28. Now that the digestive tract has been removed, you should be able to see the excretory and reproductive systems. Locate the long, brown kidneys on either side of the backbone.

29. Find the urinary bladder, which looks like a transparent sac next to the large intestine. Connecting the kidneys to the bladder, are tiny, threadlike tubes called ureters. Try to find these.

30. Find the reproductive organs in the frog. If you have a female and have removed the eggs, you also have removed the ovaries. Find the white, coiled oviducts and follow them down to the posterior end of the frog. Notice which structure they empty into. If you have a male frog, find the testes, small oval structures on top of the kidneys.

31. When you have finished dissecting your frog, dispose of it in the manner indicated by your teacher. Carefully wash and dry your dissecting tools and tray.

32. Before you leave the laboratory, wash your hands thoroughly with soap and water

Frog Dissection DAY 1 External Anatomy

Frog Dissection
Pictures:  Modern Biology, Holt

As members of the class Amphibia, frogs may live some of their adult lives on land, but they must return to water to reproduce. Eggs are laid and fertilized in water.

Describe the appearance of various organs found in the frog.
Name the organs that make up various systems of the frog.

In this lab, you will dissect a frog in order to observe the external and internal structures of frog anatomy.


  1. Put on a lab apron.     

  2. Place a frog on a dissection tray. To determine the frog’s sex, look at the hand digits, or fingers, on its forelegs. A male frog usually has thick pads on its "thumbs," which is one external difference between the sexes, as shown in the diagram below. Male frogs are also usually smaller than female frogs. Observe several frogs to see the difference between males and females.

3.      On the outside of the frog’s head are two external nares, or nostrils; two tympani, or eardrums; and two eyes, each of which has three lids. The third lid, called the nictitating membrane, is transparent. Inside the mouth are two internal nares, or openings into the nostrils; two vomerine teeth in the middle of the roof of the mouth; and two maxillary teeth at the sides of the mouth. Also inside the mouth behind the tongue is the pharynx, or throat.
Use the diagram below to locate and identify the external features of the head. Find the mouth, external nares, tympanic membrane, eyes, and nictitating membranes.

  1. In the pharynx, there are several openings: one into the esophagus, the tube into which food is swallowed; one into the glottis, through which air enters the larynx,or voice box; and two into the Eustachian tubes, which connect the pharynx to the ear.

5.    Holding the frog, cut the hinges of the mouth and open it wide.  Use the diagram to locate and identify the structures inside the mouth.  Use a probe to help find each part: the vomerine teeth, the maxillary teeth, the internal nares, the tongue, the openings to the Eustachian tubes, the esophagus, the pharynx, and the slit-like glottis.

6. Look for the opening to the frog’s cloaca, located between the hind legs.


Frog Dissection

Step-by-Step Virtual Frog Dissection

Videos below:



More Frog Dissection Videos From Other Classes: http://biotexan.livejournal.com/tag/frog

Frog Dissection VIDEOS!

Here is the private YOUTUBE link to the frog dissection video:
Frog Dissection! : http://youtu.be/6objZNkfQeM

Click here to see the Crayfish Day 2 instructions:  http://biotexan.livejournal.com/63005.html

Crayfish Dissection Day 1

Click here for the dissection instructions:  http://biotexan.livejournal.com/62949.html
Yes!  Your homework is to REVIEW for the STAAR BIOLOGY EOC test on TUESDAY -  May 5th!
Your goal should be to only miss 10 questions or LESS! (Total # of questions is 55)
NO MORE THAN 10!   I want you to have high scores!
Use your STAAR REVIEW booklet that you recieved and have been working on in class.
Use the RESOURCES linked below on this website as well!
CLICK HERE:  http://biotexan.livejournal.com/tag/staar

DISTRICT CA was last year's STAAR Biology test! It's found below:

TEST 2014 Biology   KEY 2014 Biology


Plants - Online Exit Slip

After doing the celery lab, click here to take the assessment: http://goo.gl/forms/7llbyiOIEo




Kathryn's bookshelf: read

Calling Me Home: A Novel

All She Ever Wanted

Waiting for Summer's Return

Wrapped in Rain: A Novel of Coming Home

She's in a Better Place

Lonesome Dove

Where the Heart Leads

Until We Reach Home

The Moment Between

These Boots Weren't Made for Walking

Share book reviews and ratings with Kathryn, and even join a book club on Goodreads.

Latest Month

May 2015

Kathryn's bookshelf: read

Calling Me Home: A Novel

All She Ever Wanted

Waiting for Summer's Return

Wrapped in Rain: A Novel of Coming Home

She's in a Better Place

Lonesome Dove

Where the Heart Leads

Until We Reach Home

The Moment Between

These Boots Weren't Made for Walking

Share book reviews and ratings with Kathryn, and even join a book club on Goodreads.


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