Frog Dissection Guide

Frogs belong to the class Amphibia, and live both on land and in water. One of the best ways to learn about adult amphibian anatomy is to dissect a preserved frog and see how all the organs fit together inside its body. Use this guide for complete instructions.

What You'll Need

You can get a convenient frog dissection kit, or collect the following items:

• Preserved frog specimen
• Dissection tray
• Scalpel
• Dissecting scissors
• Forceps

Look carefully at the preserved frog. Notice its powerful hind legs for jumping. The hind legs have five webbed digits (toes), while the front legs have four digits without webbing. Observe that the frog's skin is colored and spotted to help camouflage it. This coloring can change and is controlled by pigment cells in the skin called chromatophores. At the base of the frog's back, locate the anus, which is the opening from which waste, eggs, and sperm are discharged.

On the frog's head, observe the large, bulging eyes that rotate to allow sight in many directions. Frogs don't have external ears, but just behind each eye is a round, flat membrane called a tympanum (ear drum) that senses sound waves. The tympanum on females is similar in size to the eye, but much larger on males. Look for the nostrils (external nares) in front of the eyes, then open the frog's mouth to see the internal opening of the nostrils (internal nares). (Cut the hinge joints of the mouth with scissors to make it easier to open.) Near the internal nares are two vomerine teeth on the roof of the mouth. Rub your finger along the rim of the upper jaw to feel the tiny maxillary teeth. Male frogs have openings to the vocal sacs near the hinges of the lower jaw.

Frog Internal Anatomy - Dissection Guide

Click for full-size pdf

1. Lay the frog on its back, spread out its limbs, and pin them to the tray. Use forceps to lift the skin between the hind legs and make a small incision with a scalpel. Continue the cut up the center of the frog's body with scissors, being careful to cut through the skin only. Use forceps to hold the skin away from the muscle while you cut, if necessary. Make horizontal incisions just above the legs and just below the arms, then fold the resulting flaps back and pin them. (You may need to use a scalpel to help separate the skin from the muscle underneath as you fold it back.)
2. Repeat the incisions as before, this time cutting through the muscle layer to a point just below the arms. Lift the muscle with the forceps to prevent cutting the organs underneath.
3. When you reach the area just below the arms, turn your scissors and make horizontal cuts through the hard sternum. Repeat the horizontal cuts just above the arms, and then remove the bony strips entirely. Pin the remaining muscle flaps back, just as with the skin.
4. Look into the body cavity. The yellow finger-like projections on the sides are the fat bodies. It may be necessary to remove some of these in order to see the organs clearly. Likewise, a female specimen may have well-developed eggs filling the body cavity and obscuring the organs. Remove them as necessary.

Click for full-size pdf

Use this printable frog dissection diagram with labeled parts (.pdf) as a guide for locating them.

Heart. The frog's heart is the small triangular organ at the top. Unlike a mammal heart, it only has three chambers -- two atria at the top and one ventricle below. Carefully cut away the pericardium, the thin membrane surrounding the heart. Notice the arteries connected to the top of the heart, giving it a "Y" shape.

Liver. Just below the heart, the three-lobed liver is the largest organ in the frog's body.

Gall Bladder. Lift up the lobes of the liver to find the small greenish-brown sac of the gall bladder nestled between them. This stores bile produced by the liver.

Lungs. Again, lift the lobes of the liver to locate the lungs on either side of the heart. They are made of a spongy tissue.

Stomach. Curving below the liver is the stomach; it looks like a large whitish tube. After identifying the other organs, you can open the stomach and see what the frog ate. (Frogs swallow their food whole.)

Small Intestine. The stomach connects to the small intestine. The first section, or duodenum, is fairly straight, but the rest of the intestine is coiled and held in place by a blood-vessel-filled membrane called the mesentery.

Pancreas. The pancreas is a thin, flat, ribbon-like organ that lies between the stomach and the small intestine.

Large Intestine. The small intestine narrows to the point where it meets the shorter, broader large intestine. This opens into a chamber called the cloaca, the last stop before wastes exit the body through the cloacal opening, or anus. The frog's sperm or eggs also exit through the cloaca.

Spleen. Lift the small intestine to find the round, reddish spleen attached to the mesentery on the underside. The spleen stores blood as part of the circulatory system.

Ovaries. Female frogs have ovaries full of dark-colored eggs; if the eggs are well-developed, the ovaries will be very large and visible. If not, lift the stomach and intestines to see the ovaries beneath them.

Oviducts. Move the ovaries to one side to see the coiled tubes of the oviducts. If the eggs in the ovaries are not fully developed, the oviducts will be small and tightly coiled.

Kidneys. The kidneys are flat, oval-shaped organs on the back wall of the body cavity beneath the ovaries.

Testes. Male frogs have bean-shaped testes attached to their kidneys.

When you're done, print out this diagram and fill in the labels yourself to test your knowledge of frog anatomy:

• Diagram of dissected frog to label (.pdf)

learn more about frogs:

Frog Dissection Specimen Uncover a Frog Frog Hatchery Kit

Website artwork, text and images Copyright © 2013 Home Training Tools, Ltd. All rights reserved.