14.2: Amphibian (Frog) Dissection
- Page ID
- 159145
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\(\newcommand{\avec}{\mathbf a}\) \(\newcommand{\bvec}{\mathbf b}\) \(\newcommand{\cvec}{\mathbf c}\) \(\newcommand{\dvec}{\mathbf d}\) \(\newcommand{\dtil}{\widetilde{\mathbf d}}\) \(\newcommand{\evec}{\mathbf e}\) \(\newcommand{\fvec}{\mathbf f}\) \(\newcommand{\nvec}{\mathbf n}\) \(\newcommand{\pvec}{\mathbf p}\) \(\newcommand{\qvec}{\mathbf q}\) \(\newcommand{\svec}{\mathbf s}\) \(\newcommand{\tvec}{\mathbf t}\) \(\newcommand{\uvec}{\mathbf u}\) \(\newcommand{\vvec}{\mathbf v}\) \(\newcommand{\wvec}{\mathbf w}\) \(\newcommand{\xvec}{\mathbf x}\) \(\newcommand{\yvec}{\mathbf y}\) \(\newcommand{\zvec}{\mathbf z}\) \(\newcommand{\rvec}{\mathbf r}\) \(\newcommand{\mvec}{\mathbf m}\) \(\newcommand{\zerovec}{\mathbf 0}\) \(\newcommand{\onevec}{\mathbf 1}\) \(\newcommand{\real}{\mathbb R}\) \(\newcommand{\twovec}[2]{\left[\begin{array}{r}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\ctwovec}[2]{\left[\begin{array}{c}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\threevec}[3]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\cthreevec}[3]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\fourvec}[4]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\cfourvec}[4]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\fivevec}[5]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\cfivevec}[5]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\mattwo}[4]{\left[\begin{array}{rr}#1 \amp #2 \\ #3 \amp #4 \\ \end{array}\right]}\) \(\newcommand{\laspan}[1]{\text{Span}\{#1\}}\) \(\newcommand{\bcal}{\cal B}\) \(\newcommand{\ccal}{\cal C}\) \(\newcommand{\scal}{\cal S}\) \(\newcommand{\wcal}{\cal W}\) \(\newcommand{\ecal}{\cal E}\) \(\newcommand{\coords}[2]{\left\{#1\right\}_{#2}}\) \(\newcommand{\gray}[1]{\color{gray}{#1}}\) \(\newcommand{\lgray}[1]{\color{lightgray}{#1}}\) \(\newcommand{\rank}{\operatorname{rank}}\) \(\newcommand{\row}{\text{Row}}\) \(\newcommand{\col}{\text{Col}}\) \(\renewcommand{\row}{\text{Row}}\) \(\newcommand{\nul}{\text{Nul}}\) \(\newcommand{\var}{\text{Var}}\) \(\newcommand{\corr}{\text{corr}}\) \(\newcommand{\len}[1]{\left|#1\right|}\) \(\newcommand{\bbar}{\overline{\bvec}}\) \(\newcommand{\bhat}{\widehat{\bvec}}\) \(\newcommand{\bperp}{\bvec^\perp}\) \(\newcommand{\xhat}{\widehat{\xvec}}\) \(\newcommand{\vhat}{\widehat{\vvec}}\) \(\newcommand{\uhat}{\widehat{\uvec}}\) \(\newcommand{\what}{\widehat{\wvec}}\) \(\newcommand{\Sighat}{\widehat{\Sigma}}\) \(\newcommand{\lt}{<}\) \(\newcommand{\gt}{>}\) \(\newcommand{\amp}{&}\) \(\definecolor{fillinmathshade}{gray}{0.9}\)Objective/Purpose:
To observe and identify the major external and internal anatomical features of a frog as a representative model of amphibian systems (which you will later compare to mammalian anatomy).
Materials Needed:
- Preserved frog specimen
- Dissection tray and pads
- Dissection tools: scalpel, scissors, forceps, probe, pins
- Gloves, a lab coat, and safety goggles
- Disinfectant and cleanup materials
- Lab notebook for diagrams and notes
- Always wear gloves and goggles when handling specimens.
- Handle the scalpel and scissors carefully.
- Be respectful—this is a real animal that was once alive.
- Dispose of waste properly and clean tools thoroughly afterward.
Amphibian (Frog) Dissection Directions:
Step 1: Identify External Features
Place the frog on the dissection tray, observing both its dorsal and ventral sides.
Observe the following:
- Head, eyes, tympanic membranes (eardrums)
- Mouth, nostrils/external nares
- Forelimbs (front legs, with four toes) and hindlimbs (with five toes and webbing)
- Cloaca (opening for waste and reproductive fluids)
- Sex:
- Males: may have enlarged thumb pads or vocal sacs
- Females: typically larger body size; visible eggs if dissected
Step 2: Make the First Incision
- Place the frog in the dissection tray, ventral side up (belly up)
- Use scissors to make a shallow cut through the skin from the cloaca up to the chin.
- Make lateral cuts near the hind legs and arms to form flaps.
- Peel back and pin the skin open (or remove it).
Step 3: Open the Muscle Wall
- Carefully cut through the abdominal muscles along the same midline path.
- Make lateral cuts and pin back the muscle flaps to reveal the internal organs.
Step 4: Examine the Digestive System Organs
- Liver: Large, dark, multi-lobed (easily mistaken for lungs; lungs are smaller and more posteriorly located)
- Gallbladder: A small green sac under the liver
- Stomach: The curved organ on the left side
- Small intestine: A long, coiled tube
- Large intestine (colon): Leads to the cloaca
- Fat bodies: Yellowish, finger-like structures
Step 5: Examine the Respiratory and Circulatory Systems
- Lungs: Small, spongy sacs on either side near the back
- Heart: A triangular structure with 3 chambers (2 atria, 1 ventricle) located above the liver
- Blood vessels: May be faintly visible; use the probe to trace
Step 6 (Optional): Examine the Urogenital System
- Kidneys: Flat, dark organs near the spine
- Bladder: A small sac near the cloaca
Male:
- Testes: Small, white organs above the kidneys
- Sperm ducts: May run along kidney sides
Female:
- Ovaries: May contain black-and-white speckled eggs
- Oviducts: Long, coiled tubes
Step 7: Lab Skills Check (Part 1)
- Ensure everyone in your group can identify all digestive, respiratory, and circulatory structures.
- Call your instructor over. Each member of the group will be asked to identify organs at random to earn points for the skills check.
Do not dispose of your frog just yet! Keep it to observe during mammal (rat) dissection to compare structures/locations.