RAT DISSECTION NOTES
PART A – EXTERNAL FEATURES
Rinse your specimen and place on its side in the dissecting tray.
1. In the space provided, draw a diagram of your rat showing the external features. Include the
labels indicated in your lab instruction booklet.
2. Answer the following questions in the space provided.
How many toes does your rat have?
Compare and contrast the appendages and digits of the rat with those of yours. How is the rat’s
locomotion different from yours?
Determine the sex of the specimen. Make sure that you examine specimens of both sexes.
3. What is the sex of your specimen?
Sex = ____________________
PART B – INTERNAL FEATURES – RESPIRATORY SYSTEM
Locate the base of the sternum (breast bone), situated at the center of the chest. The ribs are attached
to the sternum. Use this as the starting point for your incision. With forceps, pinch the skin of the
abdomen along the mid-ventral line and draw it slightly away from the specimen. With your scissors,
make an incision in the skin. The incision should be just large enough to pass the point of your scissors
through. Now make a mid-ventral cut. This cut should extend as far forward as the hairs near the base
of the throat. Be careful not to damage the underlying body wall as you cut. Remember to keep the tips
of your scissors pointing up to avoid damaging the internal organs.
Next make two cuts from the mid-ventral line in the region of the thoracic cavity. Carefully lift the skin
and pin it to the sides of the specimen using T pins. The T pins should point away from the specimen.
Using scissors cut the ribs along the sternum, and pry them apart to reveal the organs of the thoracic
cavity.
Place the rat in the dissecting tray with its ventral surface uppermost. Spread out the limbs. Tie a piece
of string to one of the forelimbs near the ankle. Pass the string under the tray and securely tie the other
forelimb. Repeat the process with the hind limbs.
Using forceps or probe, remove the connective tissues and membranes that surround the lungs and
heart.
Expose the lungs and the trachea. Identify the following parts: ribs, lungs, diaphragm, trachea, and
larynx.
Note the difference in structure between the right and left lung.
4. In your own words, describe the structure and texture of the lungs.
Structure of Lungs
Texture of Lungs
Using a probe, move aside the layers of muscle to work deeper into the neck. If necessary, carefully cut
the muscle tissue. Locate the larynx and trachea. Trace the passage of the trachea through the throat.
Try to identify the two branches of the bronchi.
Using a small syringe or dropper, blow a small amount of air into the trachea. Note the inflation of the
lungs.
5. Complete the following table about your rat’s thoracic cavitiy.
How many lobes are there to the lungs? ______
Name the lobes of the lungs.
How many ribs are present in your rat? _______
What is the name of the thin membrane covering the lungs?
What prevents the trachea from collapsing and how is this different from the esophagus?
6. Make a drawing of the respiratory system with properly labeled parts.
7. Explain how the appearance of the following structures relates to their function as part of the
circulatory system. Give as much detail as possible, including size, texture, external structure, and
internal structure.
Structure
How structure relates to function
Trachea
Right/Left Lung
Larynx
Diaphragm
8. Using your own drawings, trace the path of air from the mouth to the lungs. Complete this on
your diagram – #6.
PART C – INTERNAL FEATURES – DIGESTIVE SYSTEM
9.
How many salivary glands does your rat have? Name each and give a brief description of each.
What is the function of the salivary glands?
Number of Salivary glands = ______________________
Salivary Gland Name
Brief Description
Function
10. Explain how the appearance of the following structures relates to their function as a part of the
digestive system. Give as much detail as possible, including size, texture, external structure, and
internal structure.
Structure
How structure relates to function
Teeth
Esophagus
Tongue
Epiglottis
11. Make a drawing and label the internal organs of your rat. You should be able to locate the
following parts: thyroid gland, heart, carotid artery, lungs, ribs, thoracic cavity, abdominal cavity,
diaphragm, liver, stomach, spleen, pancreas, small intestine, large intestine, umbilical cord, and
urinary bladder.
Locate the liver, the largest organ of the abdominal cavity.
12. Describe the appearance of the liver in your own words. How many lobes does the liver of your
rat have?
Liver Appearance:
# of Lobes = ______
Locate and describe the esophagus and note how it passes through the diaphragm just before it enters
the stomach.
13. What are the large folds in the stomach called?
The large folds in the stomach are called __________________________________.
14. Explain how the appearance and location of each part listed below is important/appropriate given
its function.
Structure
Explanation
Thyroid Gland
Heart
Carotid Artery
Lungs
Ribs
Diaphragm
Spleen
Pancreas
Umbilical Cord
Carefully cut away the connective tissue that holds the intestine together.
15. What is this connective tissue called? The small intestine is made up of three parts – identify the
three parts. What is the length of the small intestine in your rat? Why is the small intestine so
long? Cut open the small intestine using the dissecting scissors. Describe the inner surface of the
small intestine. What are these structures called?
This connective tissue is called:
The three parts of the small intestine are :
The length of the small intestine is:
The small intestine is so long because:
Description of the inner surface of the small intestine:
These structures are called:
16. Is there a gall bladder present? What is your hypothesis as to why this is?
Is there a gall bladder: YES / NO
Why?
17. Carefully cut away the connective tissue around the tract. Unravel the tract and make a drawing of
it, identifying the different portions and organs.
When done with the parts, put them aside, NOT DOWN THE SINK!
18. Explain how the appearance of the following structures relates to their function as part of the
digestive system. Give as much detail as possible, including size, texture, external structure, and
internal structure.
Structure
How structure relates to function
Liver
Pancreas
Esophagus
Stomach
Small Intestine
Large Intestine
Caecum
19. Using your own drawings of the abdominal organs, trace the path of food from the mouth to the
rectum. Identify the major steps in the digestive process that take place along the way. Complete
this on drawing #17.
PART C – INTERNAL FEATURES – CIRCULATORY SYSTEM
A special membrane covers the heart.
20. What is the name of this membrane?
Remove this thin membrane.
Carefully cut through the blood vessels a short distance from the heart. Remove the heart from your
specimen. Make an incision in the ventral surface of the heart. Your incision should expose all four
chambers of the heart.
Compare the size of the thickness of the walls of each chamber.
21. Which chambers are thicker and larger? Identify the interior of each chamber and the valves.
Locate and identify the following blood vessels: aorta, superior vena cave, inferior vena cava, pulmonary
artery, pulmonary vein, and carotid arteries.
22. Make a drawing of the circulatory system and label of each of the blood vessels. (Put the heart
back in before you do this!)
23. Explain how the appearance of the following structures relates to their function as part of the
circulatory system. Give as much detail as possible, including size, texture, external structure, and
internal structure.
Structure
How structure relates to function
Right Atrium
Left Atrium
Left Ventricle
Right Ventricle
Arteries
Veins
Heart valves
24. Using your own drawings, trace the pathway of blood from the body through the heart and back
to the body. Complete this on your diagram – #22.
CONGRATULATIONS! YOU HAVE COMPLETED YOUR DISSECTION.
PLEASE DISPOSE OF THE RATS IN THE RECEPTACLES AND THOROUGHLY WASH ALL EQUIPMENT, LAB
BENCHES AND HANDS WITH ANTIBACTERIAL SOAP. IF THERE IS TIME, WORK TO COMPLETE YOUR
DISSECTION NOTES.