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Cnidaria Exploration - A Webtour
Fish Do Not Feel Pain - Developing a Scientific Argument
Fish Feel Pain - Developing a Scientific Argument
Perch Dissection - A Supplement
Crawdad and Grasshopper Dissection - External Anatomy
Crawdad and Grasshopper Dissection - Internal
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Table of Contents
In this lab, you will dissect a frog in order to learn more about its internal and external anatomy.
As members of the class Amphibia, frogs have structural adaptations that allow them to live some of their adult lives on land, but they must return to water to reproduce. Typically, eggs are laid and fertilized in water.
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
, is transparent. Inside the mouth are two internal nares, or openings into the nostrils; two
in the middle of the roof of the mouth; and two
at the sides of the mouth. Also inside the mouth behind the tongue is the
, or throat. In the pharynx, there are several openings: one into the
, the tube into which food is swallowed; one into the
, through which air enters the
, or voice box; and two into the
, which connect the pharynx to the ear.
consists of the organs of the
digestive tract, or food tube, and the digestive glands
. From the esophagus, swallowed food moves into the
and then into the
is a digestive juice made by the
and stored in the
. Bile flows into a tube called the common bile duct, into which
, a digestive juice from the pancreas, also flows. The contents of the common bile duct flow into the small intestine, where most of the digestion and absorption of food into the bloodstream takes place. Indigestible materials pass through the large intestine and then into the
, the common exit chamber of the digestive, excretory, and reproductive systems.
consists of the
nostrils and the larynx
, which opens into two
, hollow sacs with thin walls. The walls of the lungs are filled with
, which are microscopic blood vessels through which materials pass into and out of the blood. The
consists of the
heart, blood vessels, and blood
. The heart has two receiving chambers, or
, and one sending chamber, or
. Blood is carried to the heart in vessels called
. Veins from different parts of the body enter the right and left atria. Blood from both atria goes into the ventricle and then is pumped into the arteries, which are blood vessels that carry blood away from the heart.
consists of the frog’s
kidneys, ureters, bladder, and cloaca
. The kidneys are organs that excrete
. Connected to each kidney is a
, a tube through which urine passes into the
, a sac that stores urine until it passes out of the body through the cloaca. The organs of the
system are the
testes, sperm ducts, and cloaca.
Those of the
ovaries, oviducts, uteri, and cloaca
. The testes produce
, or male sex cells, which move through
, tubes that carry sperm into the cloaca, from which the sperm move outside the body. The
produce eggs, or female sex cells, which move through oviducts into the uteri, then through the cloaca outside the body.
central nervous system
of the frog consists of the
, which is enclosed in the
, and the
, which is enclosed in the
branch out from the spinal cord. The frog’s
skeletal and muscular systems
consist of its framework of
bones and joints
, to which nearly all the
of the body are attached. Voluntary muscles, which are those over which the frog has control, occur in pairs of
flexors and extensors
. When a flexor of a leg or other body part contracts, that part is bent. When the extensor of that body part contracts, the part straightens.
1. Place a frog on a dissection tray. To determine the
, 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.
(Answer Question 1 on Lab Writeup)
Locate and identify the external features of the head. Find the
external nares, tympanum, eyes, and nictitating membranes.
(Answer Question 2 on Lab Writeup)
Looking first at the
appendages (the hind legs), identify the thigh, shank (calf), foot and toes.
(Answer Question 3 on Lab Writeup)
4. Turn the frog on its back and pin down the legs. Cut the hinges of the mouth and open it wide. Use the diagram below to locate and identify the structures inside the mouth. Use a probe to help find each part,
and point out each part to Mrs. Nash
when you have discovered it: the
, and the
(Question #5 on writeup is pointing out structures to Mrs. Nash)
1. For the internal procedure,
use this link
to guide you through the dissection and to help you identify the organs. Clicking next will lead you through each of the steps for your dissection. Please use the audio and video help when you need it. Anytime you get an opportunity to "try it" go ahead and do so.
2. Before you move on, make sure you can identify and show Mrs. Nash the following organs as well as their functions: heart, lungs, liver, gall bladder, stomach, large intestine, small intestine, spleen, fat bodies, kidneys (female-ovaries and oviducts) male (testes).
(She will initial this on your writeup, and you also need to label these organs on your writeup). (NOTE - on the diagram, the letters N, G, I, and B all refer to parts of the heart - the structures to choose from are artery, ventricle, left atrium, and right atrium - Letter E is the lower part of the stomach, known as the duodenum). (Question 7 and 8 on the writeup)
3. Removal of the Stomach: Cut the stomach out of the frog and open it up You may find what remains of the frog's last meal in there .Look at the texture of the stomach on the inside.
(Answer Question 9 on Lab Writeup)
4. Measuring the Small intestine: Remove the small intestine from the body cavity and carefully separate
from it. Stretch the small intestine out and measure it. Now measure your frog.
(Answer Question 10 on Lab Writeup)
5. Cutting about .5 inches behind the head, cut forward to attempt to find the frog brain.
(Answer the rest of the questions on your writeup)
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