Download Name Date Frog Dissection PROCEDUREs • Begin with the head of

Name _________________
Date __________________
Frog Dissection
PROCEDUREs

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
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? (look online after the
lab)

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)
You may have to look online after your done.
Human heart
Frog Heart

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?