SBI 3U1: ANIMALS: STRUCTURE and FUNCTION – Fetal pig dissection
Examining the Systems of a Fetal Pig through Dissection
Animals used for scientific research and dissection help us to understand our own bodies and how they
function in health and disease. Pigs are members of the class Mammalia and are placental mammals. The structure
and organization of the internal organs of the pig are representative of those of all placental mammals, including
humans. The fetal pig will be used as a representative mammal.
Dissection involves the careful and systematic examination of the internal structures of an organism. A
good dissection will reveal not only the location and structure of individual organs, but also how different organs
relate to one another in the various systems of the body.
Purpose:
To study the external and internal anatomy of a representative mammal to gain perspective on the
following:
 the relative location and sizes of organs.
 the interrelations between organs and organ systems.
 the scientific process of dissection and its application for anatomy and
physiology.
SAFETY PRECAUTIONS:
 The pigs are preserved in a chemical solution. Wear plastic gloves, eye
protection (goggles), and an apron at all times.
 Be aware of where to find the eye wash station and first aid kit.
 Extreme care must be taken when using dissecting instruments, particularly
scalpels and dissecting scissors. Always cut away from yourself and others
sitting near you.
 When you have finished the activity, properly clean and dry the dissection
tray and dissecting tools.
 Dispose of the fetal pig and other materials according to the teacher’s instructions.
 Clean your work area and wipe your counter.
 Wash and scrub your hands thoroughly using antibacterial soap.
Question:
What are the functional and structural relationships among the various systems of a mammal, including
the digestive, circulatory, and respiratory systems?
Materials:
- disposable gloves
- safety goggles
- lab apron
- preserved fetal pig
- string
- dissecting instruments (including scalpel, scissors, probes, and forceps)
- dissecting tray (with cover)
- ruler
- magnifying lens
- medicine dropper
- small beaker (to act as a waste disposal container)
- paper towels
- newspaper (to line counter tops)
PART 1: External Anatomy
Procedure:
1.
Put on protective gear (safety goggles and apron).
2. Obtain a fetal pig. Dry your fetal pig with paper towel. Place your pig on its side in the dissecting tray.
3. The fetal pig has four main body segments: the head, neck, trunk, and tail (Figure 1).
(a)
(b)
Figure 1
Lateral (side) views of a fetal pig.
4. Using a ruler, measure the length of your fetal pig from the snout to the base of tail. Use the graph in
Figure 2 to estimate the gestational age of the fetal pig. Record estimate on answer sheet.
Figure 2
Age/size ratio for fetal pig.
5. Turn your pig on its back (dorsal surface) and observe the pairs of nipples along the front (ventral surface).
Both male and female fetal pigs have these nipples.
6. Use Figure 3 to determine the sex of your fetal pig.
- In females, the urogenital opening is located slightly ventral to the anus. A small, spiked tissue, often
called the genital papilla, projects from the urogenital opening.
- In males, the scrotom containing the testes can be located just ventral to the anus. The urogenital opening
of the male is found immediately posterior to the umbilical cord.

What is the sex of your fetal pig?
Figure 3
(a) Female fetal pig
Record the sex on the answer sheet.
(b) Male fetal pig
PART 2: Internal Anatomy
Throughout the dissection, you will be directed to examine specific organs as they become visible. It is
important to follow the directions carefully and to only remove those organs indicated by the procedure.
Proceed cautiously.
THE DIGESTIVE SYSTEM
A. ABDOMINAL CAVITY
Procedure:
7. With the pig still on its dorsal surface (back), attach one piece of string to the pig’s left ankle. Pull it under
the dissecting tray and tie it tightly to the right ankle. Attach another piece of string to the pig’s left wrist.
Pull it under the tray and tie it tightly to the right wrist. Ensure that the strings are pulled tightly so the
limbs are well spread out and that the pig’s front (ventral surface) is well exposed.
8. To effectively expose the abdominal cavity and its organs, follow ONLY the incision (cutting) lines
indicated below. Use Figure 5 as a guide.
The first incision #1:
Select a point just anterior (towards head end) to
the umbilical cord on the pig’s ventral surface.
Using forceps, pinch the skin of the abdomen
along the midventral line and pull it slightly
away from the animal. With your scissors, make
an incision in the skin, large enough to pass the
point of your scissors through. To avoid
damaging the organs as you cut, keep the tips of
the scissors pointing up. Be careful not to
damage the umbilical cord.
The second incision #2:
Make a second incision around the base of the
umbilical cord extending back to just anterior to
the anus. You may wish to turn your specimen
around so you can cut away from you. Repeat
on the other side.
The third incision #3:
Locate the base of the sternum (breast bone),
situated in the centre of the chest. The ribs are
attached to the sternum. Select a point slightly
posterior to the sternum and cut across the
ventral surface. The incision should be posterior
to the diaphragm, which you will be able to see
as a dome-shaped layer of muscle separating the
abdominal and thoracic cavities. Cut and extend
laterally on both sides of the pig, as far down the
sides towards the dissecting tray.
The fourth incision #4:
Make two final horizontal incisions, one on each side
of the #2 cuts, bordering the umbilical cord and just
anterior to the hind limbs. Cut as far down the sides
towards the tray.
Figure 5
Incisions through ventral surface
of fetal pig to expose the abdominal cavity.
9. Fully expose the abdominal cavity by cutting off the flaps along incision #3 and incision #4.
10. The organs of the abdomen (Figure 6) are covered and
protected by a membrane called the peritoneum. The
double-layered sheets of peritoneum are called
mesenteries. Using forceps or a dissecting probe, gently
move the mesenteries aside to reveal the underlying
organs.
Figure 6
Abdominal cavity of fetal pig
and the organs of digestion.
Liver and Gallbladder
11. Locate the liver. The liver appears a dark red or brown colour because it is engorged (filled) with blood.
The liver contains 20% of the total blood supply in the fetal pig’s body at any given time. Identify two
functions of the liver. Record your answer on the answer sheet.
12. Using a probe, lift the lobes of the liver and locate the greenish, sac-like gallbladder. Locate the common
bile duct (you may have to remove some mesentery to see it). Describe the specific location of the
gallbladder. Which portion of the small intestine does the gallbladder connect to? Record your
responses on the answer sheet. Take a moment and try to locate this connection.
Stomach
13. Locate the stomach, underneath the liver, on the left side. Using a probe, lift the stomach and locate the
esophagus attached to the anterior (top) end of the stomach (note how the esophagus passes through the
diaphragm just before it enters the stomach). Locate the small intestine attached to the posterior (bottom)
end of the stomach.
Pancreas
14. Using a probe, lift up the stomach and push away the small intestines. Locate the pancreas (finger-shaped
and creamy-white in colour), seen toward the back wall of the abdominal cavity behind the stomach and
small intestines. What vital substances does the pancreas provide? Into where and through what does
the pancreas secrete these substances? Record your responses on the answer sheet.
Spleen
15. Locate the spleen (elongated organ), found toward the left side, around the outer curvature of the stomach.
The spleen is one of the organs of the lymphatic system.
Small and Large Intestines
16. Locate the small intestine. Move to the distal end of the small intestine and locate the point on the left side
of the abdominal cavity where the large intestine begins. Toward the end of the large intestine is the
rectum. Note where the tract terminates at the anus. Compare the structures of the small and large
intestines. How is the small intestine different from the large intestine? Record your response on the
answer sheet.
TEACHER EVALUATION
17. Before proceeding, you must complete a teacher evaluation. Each member of the group will be
asked, independently, to locate various organ structures and answer specific questions. Please ensure that
all group members are familiar the abdominal cavity. Call your teacher over when the group is ready.
ORGAN REMOVAL
18. Cut the esophagus as close to the top of the abdominal cavity as you can. Make a second cut as close as you
can to the end of the digestive tract near the anus. Carefully remove the entire digestive tract, in one piece,
from the specimen.
19. Remove the stomach by making transverse (crosswise) cuts near the top of the stomach where it connects to
the esophagus, and near the bottom of the stomach where it connects to the small intestine.
20. Make a cut from the top to the bottom of the stomach, and open it up. Very gently, rinse the inside of the
stomach. Use the magnifying hand lens to view the inside of the stomach. Describe the appearance of the
inner lining of the stomach. How does its appearance relate to its function? Record your description
and response on the answer sheet.
21. Remove the intestines (small and large). Carefully use your scissors to snip away the mesentery tissue
around the intestines. Gently unravel the small intestine ONLY. How long is your pig’s small intestine?
(use your ruler to measure it in cm). Record your measurement on the answer sheet.
THE CIRCULATORY and RESPIRATORY SYSTEM
B. THORACIC CAVITY
Procedure:
22. To effectively expose the abdominal cavity and its organs, follow ONLY the incision (cutting) lines
indicated below. Use Figure 7 as a guide.
The first incision #1:
Pick a point above incision #3 (the base of the
sternum). Using forceps, pinch the skin of the
abdomen along the midventral line and pull it
slightly away from the animal. With your scissors,
make an incision in the skin, large enough to pass the
point of your scissors through. Have the cut (#1)
extend as far forward as the hairs near the base of the
throat. To avoid damaging the organs as you cut,
keep the tips of the scissors pointing up. Cut near the
neck, outward towards the sides of the pig
The second and third incision #2 & #3:
Make two cuts (#2 and #3) from the midventral line
in the thoracic cavity region. Have these cuts extend
fully down the sides of the pig to the dissecting tray.
You are cutting through the skin first. Cut off the
skin flaps.
23. Using a sturdy pair of dissecting scissors, cut the ribs
along the sternum (midline of the thoracic cavity),
and pry them apart to reveal the organs of the
thoracic cavity.
24. Expose the thoracic (chest) cavity by cutting off the
rib flaps that cover the thoracic cavity. The thoracic
cavity is the area between incisions #2 and #3.
25. Using forceps or a dissecting probe, remove the connective
tissues and membranes that surround the lungs and heart.
Figure 7
Incisions through ventral surface of fetal
pig to expose thoracic cavity.
26. The heart is found between the two lungs and is
protected by the rib cage. The heart is surrounded by a
thin and transparent film of connective tissue called the
pericardium. Identify the organs of the thoracic cavity
as shown in Figure 8.
Figure 8
Organs of the Thoracic cavity.
The Heart & Circulatory System
27. Note the location of the heart in the thoracic cavity. In what ways is the heart protected from damage?
Record your response on the answer booklet.
ORGAN REMOVAL
28. Carefully remove the heart from the thoracic cavity. Be careful not to damage the lung tissue. You may
need to tease away any connective tissue. Hold the heart in your hand and orient it as it would appear in
the fetal pig, as it appears in the ventral (front) view in Figure 9. Note the large vessel that traverses
(crosses) the front (ventral surface) of the heart. This is the coronary artery. What role does the coronary
artery play? Record your response on the answer booklet.
29. Locate the superior and inferior vena cavae, pulmonary arteries and veins, and the aorta.
Refer to Figure 9 for assistance.
(c)
Figure 9
(a) Ventral (front) view.
(b) Dorsal (back) view.
(c) Cross-sectional view.
30. Internally the heart is separated in to a right and left side. What is responsible for this separation?
What type of tissue makes up the majority of the heart organ? Record your response on the answer
booklet.
The Lungs & Respiratory System
31. Locate the lungs and the trachea leading into the lungs. Refer to Figures 8 & 10.
Figure 10
Ventral (a) and Dorsal (b) views
of the lungs.
32. Note the difference in structure between the right and left lungs. What is the most obvious difference?
How can you account for this difference? Record your responses on the answer sheet.
33. 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, trachea, and esophagus. Describe the difference in structure between
the trachea and esophagus. Record your responses on the answer sheet.
34. Note the cartilaginous rings of the trachea. What function do these rings serve? Record your response
on the answer sheet.
35. Examine the rib cage and try to identify the external and internal intercostals muscles.
36. Trace the passage of the trachea down towards the lungs. Try to identify the branching of the right and left
bronchi.
37. Locate the esophagus. Where is it located with respect to the trachea? Record your answer on the
answer sheet.
38. Locate the diaphragm, seen just beneath the lungs. What is its function? How will it move during
inhalation? Record your responses on the answer sheet.
ORGAN REMOVAL
39. Attempt to remove the lungs with the trachea attached (as seen in Figure 10).
40. Using a dropper, push/squeeze a small amount of air into the trachea. Note the inflation of the lungs.
Using arrows and a flow chart method, illustrate the pathway of air from the lungs to the oral cavity.
Record your response on the answer sheet.
41. Make a lateral cut across one of the lungs. Note the appearance of tiny holes. These are the bronchioles
which have been cut and would eventually lead to the alveoli. Describe the texture of the lungs? Record
your response on the answer sheet.
TEACHER EVALUATION
42. You must complete a teacher evaluation. Each member of the group will be asked, independently,
to locate various organ structures and answer specific questions. Please ensure that all group members are
familiar the thoracic cavity and the organs removed from this cavity. Call your teacher over when the
group is ready.
CLEAN-UP
43. Wash all dissecting instruments, rulers, magnifying lenses and dissecting trays at YOUR bench’s sink.
44. Ensure that all the above material are clean and DRY and return them to their indicated locations.
45. Using the newspaper or plastic lining your bench, wrap up your pig and waste products and dispose of
them in the garbage bags at the front of the class. Ensure that all gloves and paper towels are also
disposed of in these bags.
46. Wipe down your lab bench with water.
47. Ensure your sink is clean and that there are no scraps from the pig left in it. If there are, remove them
using a paper towel and rinse out the sink.