Frog External Anatomy - Teacher's Guide

Original Document: Frog External Anatomy

This lab is a good starter lab for the frog. It's short and allows the teacher to talk about general principles of dissection, rules, and clean-up protocols. This usually takes students about 20-30 minutes to complete. Students should wear safety goggles, latex gloves are optional.

The hardest part for students is opening the jaw, you really must apply a lot of pressure to force the jaw open, this is usually accompanied by the sound of bone cracking.

For whatever reasons, students are fascinated by the eyes. I included the statement "you may remove the eye" because so many of my students in the past have asked if its okay to do so. And yes, the frog eyes do bounce (a little) and they are hard to the touch, not squishy like you might imagine.

Student guide has checkboxes, it is helpful for students to check the boxes as they complete the dissection to keep them on task and at the appropriate step.

1. Observe the dorsal and ventral sides of the frog.
Dorsal side color __dark __ Ventral side color _light_______

2. Examine the hind legs.
How many toes are present on each foot? ____5__
Are the toes webbed? __yes___


3. Examine the forelegs.
How many toes are present? __4_____Are the toes webbed? _no____

4. Use a ruler to measure your frog, measure from the tip of the head to the end of the frog's backbone (do not include the legs in your measurement). Compare the length of your frog to other frogs - most frogs are 10 - 15 cm in length

frog measuring

5. Locate the frog's eyes, the nictitating membrane is a clear membrane that attached to the bottom of the eye. Use tweezers to carefully remove the nictitating membrane. You may also remove the eyeball.
What color is the nictitating membrane? ___clear or white/beige___ What color is the eyeball? ______yellow_______

frog eyes

6. Just behind the eyes on the frog's head is a circular structure called the tympanic membrane. The tympanic membrane is used for hearing. Measure the diameter (distance across the circle) of the tympanic membrane.
Diameter of tympanic membrane __about 1 cm

frog head

7. Feel the frog's skin. Is it scaley or is it slimey? ___slimey_____

Anatomy of the Frog's Mouth

Procedure: Pry the frog's mouth open and use scissors to cut the angles of the frog's jaws open. Cut deeply enough so that the frog's mouth opens wide enough to view the structures inside.

frog mouth

1. Locate the tongue. Play with the tongue. Does it attach to the front or the back of the mouth? _front___ (You may remove the tongue)

Insert a probe into the Eustachian tube. To what structure does the Eustachian tube attach? tympanic membrane (ear)

Structure Function Location
Vomerine Teeth holding prey roof of mouth
Eustachian Tubes equalize pressure angles of jaw
Tympanic Membrane hearing behind the eyes
Esophagus swallowing food back of the mouth
Glottis airway behind tongue
Tongue capturing prey bottom of mouth