Frog Dissection: Labeled Anatomy and Lab Guide

Use this frog dissection guide to identify external features and major internal organs, connect each structure to a function, and record observations from a preserved specimen. The labeled diagrams and photographs below support a high school biology lab or a diagram-based alternative.

Student resource: Frog Dissection Worksheet. The guide and worksheet have different jobs: this page supports identification; the worksheet asks students to explain pathways and functions.

Learning goals and materials

  • Use dorsal/ventral and anterior/posterior directions to orient a specimen.
  • Locate major structures and explain how organs work together.
  • Distinguish an observation from a conclusion based on a diagram or reference.

Prerequisites: basic tissues, organ systems, and vertebrate classification. Materials: preserved frog, dissecting tray, appropriate PPE, blunt probe, forceps, teacher-approved scissors and pins, and a notebook or the worksheet. Teachers should preview the specimen and decide which structures students can realistically identify.

Teacher preparation and safety

This guide is for commercially preserved specimens under teacher supervision. Review the specimen label, supplier’s safety data sheet (SDS), school risk assessment, and disposal rules. Demonstrate tools before students begin. Use the required splash goggles, preservative-compatible gloves, protective clothing, and ventilation. Keep hands out of the cutting path and use a tray; no food or drink.

Offer a diagram, model, or teacher-demonstration route when needed. Keep specimens and preservative out of sinks and ordinary waste unless the school’s approved procedure permits it. Clean equipment and surfaces as directed and wash hands. Begin with the biology lab safety expectations. See NSTA’s dissection safety guidance and the supplier’s dissection FAQs; product-specific instructions take priority over a general web guide.

Labeled frog internal anatomy

Start with the diagram before opening a specimen. When a frog lies on its back, its anatomical right is on the viewer’s left. Preservation, species, and reproductive condition affect appearance; do not identify an organ by color alone.

Labeled frog body cavity showing heart, lungs, liver, stomach, intestines, gallbladder, pancreas and cloaca
Legacy internal-anatomy diagram. Pair the labels with the function table; the drawing simplifies the position and shape of real tissues.

Legacy diagram credit retained from the original resource: Modern Biology, Holt. Open an image to view its original file; some legacy labels are small.

External anatomy and mouth structures

External frog head diagram labeling nares, eyes, tympanum, nictitating membrane and mouth
The tympanum is associated with hearing. The nictitating membrane is a protective eyelid.

Locate the eyes, external nares, tympana, forelimbs, and hindlimbs. Note skin texture and limb proportions without generalizing from one preserved specimen to every frog. Some adult males have prominent nuptial pads used during mating; prominence and body size vary with species and condition, so use several traits rather than size alone to infer sex.

Compare the original male/female forelimb drawings
Original male frog forelimb drawing with enlarged thumb pad
A nuptial pad can be a useful clue in the species illustrated; it is not a universal sex test.
Original female frog forelimb drawing
Compare with the male illustration and your teacher’s species-specific reference.
Legacy mouth labels beside a simplified frog incision illustration
Mouth labels include internal nares, vomerine teeth, maxillary teeth, glottis, and esophagus. The incision sketch is a legacy illustration, not a substitute for the teacher’s specimen-specific cutting demonstration.

With the mouth opened as the teacher directs, distinguish the glottis from the larger opening into the esophagus. In commonly used toothed frog specimens, maxillary teeth form a row along the upper jaw and vomerine teeth occur in patches on the roof of the mouth. They help hold prey rather than chew it like human molars; the original description of only “two maxillary teeth” should not be used.

A step-by-step observation sequence

  1. Orient and record: sketch the intact specimen, mark directions, and identify external features. Use the diagram route if no specimen is used.
  2. Inspect the mouth: use the teacher’s opening method and a blunt probe to locate the structures above. Do not force the jaws or cut mouth hinges without instruction.
  3. Expose the body cavity: the teacher demonstrates opening the skin and then the body wall. Lift tissue away from underlying organs and make only shallow, controlled cuts with approved tools. Keep the heart and viscera intact; stop for help if the next layer is unclear.
  4. Identify before moving: locate the liver, heart, stomach, intestines, and lungs using position and connections. Record what is actually visible. Eggs or fat bodies may obscure other organs.
  5. Trace connections: with permission, gently move a structure to follow the digestive tract. Do not remove organs simply to match the drawing. Preserve the specimen for later observations if that is the class plan.
  6. Check deeper structures only if assigned: examine the dorsal kidneys and reproductive structures with teacher guidance. A visible spinal nerve is not the spinal cord. Brain, nerve, and muscle investigations require a separate approved procedure.
  7. Finish: complete observations, follow the school’s storage/disposal procedure, clean the station, and wash hands.

Major organs and what to look for

Structure Identification and function
Heart and lungs The typical adult frog heart has two atria and one ventricle. Lungs lie to either side; adult frogs also exchange gases through skin and the mouth lining.
Liver and gallbladder The large liver overlies other organs. It produces bile; the gallbladder stores it. Bile enters the intestine rather than serving as a food passage through the liver.
Stomach and intestines Follow esophagus → stomach → small intestine → large intestine → cloaca. The small intestine is a major site of digestion and nutrient absorption.
Pancreas A thin gland near the stomach and the first part of the small intestine; it supplies digestive enzymes and has endocrine functions.
Spleen A small organ associated with circulation and immune function. Do not call it a digestive gland just because it lies near the intestine.
Kidneys, ureters, and bladder Kidneys lie along the dorsal body wall. Ureters drain to the cloaca; the bladder communicates with the cloaca and can store urine. It is not a direct ureter-to-bladder arrangement like the familiar mammalian pathway.
Gonads and fat bodies Testes or ovaries are reproductive structures. Fat bodies store energy. Eggs may occupy much of a female’s body cavity, and tissue condition varies.
Preserved frog photograph identifying the stomach and pancreas
Identify the pancreas by its relationship to the stomach and intestine; preservation can alter color.
Preserved frog photograph labeling fat bodies, spleen, and small and large intestines
Use the connections as well as the labels to trace the digestive tract.
Additional original photo and urogenital diagram
Additional original photograph of frog intestines, spleen and fat bodies
The legacy resource includes this similar digestive-system view; compare positions rather than treating it as a different organ system.
Side-by-side male and female frog urinary and reproductive-system diagrams
Simplified legacy diagrams: compare kidneys, gonads, ducts, bladder and cloaca. Use the corrected urinary-pathway note above when interpreting the drawing.

Teaching notes and checks for understanding

  • Ask students to record “not visible” rather than invent an observation. A diagram label is not proof that the organ was found.
  • Discuss why a shared cloaca does not make digestion, excretion, and reproduction the same process.
  • Use the existing worksheet with the corrected anatomy notes. Its egg-number example is a particular scenario, not a claim about every frog species. No newly verified answer key is supplied for the legacy questions.

Original check: A student traces food through the liver and then the stomach. What needs correcting? Food travels through the gut; liver secretions aid digestion without making the liver part of the food tube. Original check: Does a preserved specimen prove how blood or urine flows in a living frog? No. Observation of structure supports a model of function, which should be checked against a reference.

Continue the comparison

Compare this vertebrate with the Clam Dissection guide: both have digestive organs, but their body plans and feeding structures differ. Return to Animal Dissections for the existing resource directory.

Sources and further reading