Name_____________________
ASSIGNMENT
 Conduct a Frog Dissection.
 Include labeled diagrams of your frog.
 Answer all questions from the lab packet and describe each organ.
PROCEDURE
 Begin with the head of the frog. The two holes near the mouth end of the head are the external nares, the outer nose openings.
1. How is the location of the external nares an adaptation to living in water?
 Just behind the eyes are the eardrums, which are round, flattened areas in the skin.
 To examine the interior of the mouth, use scissors to cut he edges of the mouth at each hinge joint. In other words, where the maxilla (upper jaw) and the mandible (lower jaw) join together. Open the mouth wide.
 Rub your finger along the roof of the mouth. You will feel a row of small teeth called maxillary teeth. Below these are two sharp mounds called vomerine teeth. Close to the teeth are two openings, the internal nares.
2. Where do you think these openings lead?
 The wide opening in the center of the mouth is the top of the esophagus, the tube that leads to the stomach. Below the esophagus is the vertical slit called the glottis, which leads to the lungs.
 The frog's tongue fills most of the lower jaw. In the living frog, the tongue is sticky.

3.
What is unusual about where the frog's tongue is attached compared to where your tongue is attached?
4.
How would this place of attachment and the tongue's stickiness be useful to the frog?
 Place the frog in the pan with the ventral (belly) side up.
With forceps, pick up the loose skin just above the anal opening. Using scissors cut through the raised skin. Cut the skin along the center of the body to the base of the head. Cut laterally from the central cut to each of the limbs.
 Now make the same cuts through the muscle of the body wall as you did through the skin. Raise the body wall with the scissors to avoid damaging the structures below.
When you reach the forelimbs, you will have to cut through the sternum, the bone that connects the forelimbs. At this point you may have to pin the muscle back so you can see the insides.
 In order to fully examine the internal organs, you will probably have to remove certain structures. A large mass of black and white eggs may fill much of the abdomen. If so, you have a female. If there are no eggs you may or may not have a female. Carefully remove the egg mass and throw them in the wastebasket.
 There may also be several yellow finger-like structures.
These are fat bodies. The fat bodies store food which is used during periods of inactivity, e.g., winter.
 In the middle of the body cavity is the liver, the largest organ of the
 Body. The reddish - brown liver consists of 2 large lobes with a smaller lobe between them. The liver produces bile, which aids in the digestion of fats. The liver also stores food in the form of glycogen and plays a role in the breakdown of poisonous wastes.
 Carefully lift the liver to see the other organs of the digestive tract. On the underside of the liver is a greenish sac called the gall bladder. This stores the bile produced by the liver before it passes into the small intestine.

 The oval, whitish structure on your right hand side is the stomach, where the food is partially digested. At its top end, the stomach is connected to the esophagus, which channels food from the mouth. At its bottom end, the stomach narrows to a bugle called the pyloric valve. Run your finger over this valve; it should feel like a knot. When this donut-shaped muscle contracts, food is prevented from leaving the stomach.
 The small intestine is the narrow tube leading away from the stomach. Digestion is completed in the small intestine, as is most nutrient absorption. The small intestine loops in tight coils down to the large intestine, a short, wide intestine. The large intestine leads to the cloaca, a large sac that passes wastes out of the body. Cloaca in Latin means "sewer."
 A this point you will need to draw and to label several structures that should now be visible:
Liver
Large intestine
Small intestine
Cloaca
Stomach
Fat bodies
Heart
 Locate the small pair of lungs.
5. Why are the lungs so small in this organism?
 Find the heart in the center of the chest cavity between the lungs. Notice the heart lies in a thin sac called the pericardium. (It may be torn open in some specimens.)
6.
What is the function of the pericardium?
 Remove the pericardium to observe the 3 chambered heart.
The two dark walled chambers are atria. The right atrium receives deoxygenated blood from the veins of the frog's body. The left atrium receives oxygenated blood from the lungs. Both atria empty into a common ventricle, which is the lighter colored thick-walled part of the heart. The large vessel forming an Y-shaped at the anterior end of the ventricle is the conus arteriousus. Blood is pumped out of the

conus arteriosus through a system of arteries you see around the heart.
7.
Compare the frog heart with the human heart (Make a T chart)
 Remove the liver and record its mass.
 Lying just under the curved end of the stomach is the thin ribbon-like pancreas. This structure is very difficult to find for some people.
 Cut out the stomach and open it up. What was in the stomach?
 Cut out the large and small intestines. Measure and record each in centimeters.