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PIG DISSECTION
By Gwen Hale and Lee Perry
Summary:
Pigs are mammals just as humans are. A study of the pig anatomy will allow
high school students to better understand the human body. The following is a
description of how to dissect a fetal pig.
Objectives:
1. The student will be able to identify the external and internal features of the
pig.
2. The students will learn the unique functions of the organs.
Instructions:
Students may wish to wear gloves and goggles while dissecting. All
dissected pig parts should be placed in appropriate containers. After the lab
the students should dispose of the fetal pigs, latex gloves, and any other
waste according to their teacher's directions. Also dissecting equipment
should be washed according to the teacher's directions.
Section 1- External observations
General Observations
1. Identify the four regions of the fetal pig body: the large, compact head; the
neck; the trunk with four appendages.
Head and Neck Region
1. Examine the head in more detail. Identify the eyes with upper and lower
lids, the external ears, the mouth, and the nose or snout. Note the position
of the nostrils or external hairs on the snout. Feel the texture of the snout. It
is composed of bone, cartilage, and other tough connective tissue and as
such, allows the pig to root and push soil and debris in its search for food.
2. Open the pig’s mouth and note the tongue with its covering of papillae,
which contain taste buds. Papillae are especially concentrated and prominent
along the posterior edges and tip of the tongue. Notice if any baby teeth are
present.
Appendages
1. Examine the feet and legs of your pig. The first toe, or digit, corresponds
to your big toe or thumb. The second and fifth digits are reduced in size, and
the middle two digits, the third and fourth, are flattened or hoofed. Pigs and
other hoofed animals walk with their weight of the tips of the digits.
2. Locate and identify the following structures and joints: wrist, elbow,
shoulder, ankle, knee, and hip.
Trunk
1. Place the pig on its dorsal surface and examine its abdomen. (Do not tie or
pin the pig down yet!) The most prominent feature of the ventral surface of
the fetal pig is the umbilical cord seen near the posterior end of the
abdomen. During its development, the fetus was connected to the placenta on
the uterine wall of its mother’s reproductive system via the umbilical cord.
2. On the ventral surface of the pig the pairs of nipples or teats. Both male
and female pigs may have from five to eight pairs of these structures. Finally
locate the anus, the posterior opening of the digestive tract. The anus is
situated immediately under the tail.
Determine the sex of your fetal pig.
1. The male is identified by (1) the presence of a single urogenital opening to
the urinary and reproductive system just behind the umbilical cord. (2) the
presence of a swelling on the posterior portion of the abdomen between the
upper ends of the hindlimbs. The swelling is the scrotum, which contains the
testes, a part of the male reproductive system. Identify the penis, a large,
tubular structure immediately under the skin posterior to the urogenital
opening.
2. The female is identified by the presence of a single urogenital opening
immediately ventral to the anus. A small fleshy piece of tissue, the genital
papilla, projects from the urogenital opening.
*Note that in both male and female fetal pigs, there is a common urogenital
opening shared by the urinary tract and the reproductive system.
Section 2- Internal observations of oral cavity
1. With scissors, carefully cut through the corner of the mouth and back
toward the ears until the lower jaw can be dropped and the oral cavity is fully
exposed.
2. If teeth are not present, cut into the gums and determine whether
developing teeth are present.
3. Feel the roof of the oral cavity and determine the position of the hard
palate and soft palate. (In your own mouth you can feel your hard and soft
palates by touching the superior surface of the interior of your oral cavity
with your tongue. The anterior portion is your hard palate. Posterior to the
hard palate is the soft palate.) Posterior to the soft palate is the pharynx.
Locate the opening to the larynx, the glottis. It can be identified by the
presence of a small white cartilaginous flap, the epiglottis on its ventral
surface. The glottis is between the tongue and the esophagus. The epiglottis
covers the glottis when a mammal swallows. If you are struggling to find the
larynx and pharynx, they can be located later, after you open up the visceral
cavity and dissect the throat region.
Section 3 -Opening of the visceral cavity
1. Place the pig, ventral side up, in the dissection pan. Secure the pig by
using rubber bands, string or pins. Begin your incision with scissors at the
umbilical cord and proceed towards the chin. You should cut through the
muscle layer but not too deeply; otherwise the internal organs may be
damaged.
2. If your pig is a female, make the second incision completely around (to
either side of) the umbilical cord and proceed with a single incision
posteriorly for approximately 3 cm between the hindlimbs.
3. If your pig is a male, make the second incision as a half circle anterior to
the umbilical cord and then proceed with two incisions posteriorly, and at
angles, to the region behind the hindlimbs. The incisions made in the region
of the scrotum should be made carefully so as not to damage the testes, lying
just under the skin.
4. Deepen incisions until the body cavity is exposed. Proceed carefully,
however, as the body cavity may be filled with a dark fluid. In order to make
lateral flaps of the muscle tissue (which can be folded out of the way) make
incisions as illustrated.
Now, carefully open the body cavity. If it is filled with fluid, pour the fluid
into the waste container provided (not into the sink) and carefully rinse out
the cavity with a little water.
5. Use your finger to locate the lower margin of the rib cage. Just below it,
make an incision laterally in both directions from the first incision. In this
region is the diaphragm, a sheet of muscular tissue connected to the body
wall and separating the two major body cavities: the thoracic cavity and the
abdominal cavity. By using your scalpel, free the diaphragm (do not remove
it) where it is in contact with the body wall.
6. Carefully peel back the side flaps and pin them beneath your pig. It may
be necessary to cut through the ventral part of the rib cage with a pair of
scissors to separate body wall flaps. Do not damage the heart and lungs.
7. To free the umbilical cord and the flesh immediately surrounding it, cut
through the umbilical vein and attached tissue. Pin this flap between the hind
legs.
8. When the body cavities are fully exposed, carefully remove any excess red
or blue latex that may be present.
Section 4- Identifying the organs
Endocrine system
Thymus gland, a whitish
structure that is divided
into two lobes and is in
the neck and upper
thoracic cavity, it partially
covers the anterior portion
of the heart and extends
along the trachea to the
larynx. It plays an
important role in the
development and
maintenance of the
immune system.
2. Thyroid gland, immediately beneath the thymus in the neck region, small
and reddish, oval shaped and a more solid consistency than the thymus.
Thyroid hormones function in the regulation of metabolism, growth, and
development.
Digestive System
1. Liver, consisting of four reddish brown lobes, is located in the visceral
cavity posterior to the heart. The liver is a vital organ, serving as the filter
and storage organ. It produces bile.
2. Gallbladder: can be found on the undersurface of the pig's right central
liver lobe. The gall bladder is a small, greenish sac and is attached by
membranous tissue to the underside of a lobe of the liver. Bile is stored here.
It is used for breaking down fats . The bile duct passes from the gallbladder
to the small intestine where the bile enters the digestive tract.
3. Pancreas, carefully move
the small intestine, elongated
granular mass located
between the stomach and the
small intestine. This organ
supplies digestive enzymes
into the intestine and
hormones into the blood.
4. Stomach, a whitish, saclike organ located under the
left lobe of the liver. It
frequently extends posterior
to the liver before opening
into the small intestine. Note that the esophagus penetrates the diaphragm
before joining the stomach. Feel for the cardiac (cardioesophageal) sphincter
and the pyloric sphincter by gently squeezing the entrance and exit of the
stomach between your index finger and thumb. (You might need to use the
index of your text book to help you find out where the cardioesophageal and
pyloric sphincters are.) The stomach serves as the first organ of digestion.
Make a cut in the stomach to expose its contents. The rough surface is called
rugae.
5. Small intestine, small tubular extension of the digestive tract serving as the
area for final digestion and absorption.
6. Mesentery, transparent membranes holding the coils of the small intestines
together.
7. Large intestine, the enlargement following the small intestine which
extends into the pelvic region. The coiled large intestine terminates into the
straight rectum. The large intestine is used for the storage of wastes and the
removal of water. To locate the rectum you will need to remove a great deal
of muscle tissue, working downward toward the dorsal surface. But, wait to
do this until you reach the urogenital part of the dissection.
Respiratory System
1. Larynx, located anterior to the heart, air passes through the glottis into the
larynx. In humans it is the voice box. Make a vertical slit in the larynx to
expose the vocal chords.
2. Trachea, extends from the larynx and divides into two major branches, the
bronchi, to the lungs. Note the cartilaginous rings that prevent the trachea
from collapsing. Once exposed, the trachea is easy to identify because it
looks and feels just like a vacuum cleaner hose. FORM FOLLOWS
FUNCTION!
3. Lungs, the reddish purple sacs that are found on either side of the heart
dorsal to the liver. Note the right lung consists of four lobes and the left two
or three lobes.
Circulatory System
1. Heart, consists of two atria which have thinner walls and are darker than
the ventricles, reddish in color, is enclosed within a pericardial sac. It serves
as the pump for the blood. The pericardial sac, which surrounds the heart,
may be filled with latex. Remove it with your forceps. Remove the
pericardial sac to view the heart.
2. Coronary artery and coronary vein, are lying in a diagonal groove
between the two ventricles. They supply blood directly to the heart.
3. Superior vena cava and inferior vena cava, gently push the heart to the
right and identify these veins.
4. Aorta, leads dorsally out of the left ventricle of the heart and its base is
partially covered by the pulmonary trunk coming from the right ventricle.
5. Spleen, reddish-brown spherical organ located posterior and dorsal to the
stomach. This organ is a filter for the removal of red blood cells and the
production of antibodies.
Urogenital System
1. Kidneys, situated against the dorsal
wall, are covered by peritoneum, the
smooth shiny membrane that lines the
abdominal cavity. To expose the right
kidney and ureter, lift up the
abdominal organs and move them
anteriorly to the pig’s left. Using a
dissecting needle, carefully scrape
away the peritoneum so that the
kidney, a largish, bean-shaped
structure can be seen.
2. Bladder, follow the ureters to the bladder. Then lift the bladder and find
the urethra. the urethra is the structure through which urine passes from the
bladder to the outside of the animal. In the male, the urethra is very long and
passes through the penis to the outside of the body. In the female, the urethra
is short and passes posteriorly to join with the vagina.
3. Ovaries, (female) small, yellowish kidney-shaped structures that lie just
posterior to the kidneys. They are the site of egg production and female
hormones. All of the eggs are present at birth.
4. Uterus and vagina, (female) next to the urethra, also tube-like, the uterus
will be anterior to the vagina which is a muscular thick wall. You can find
the uterus by tracing the fallopian tubes from the ovaries.
5. Testes, (males) site of
sperm production; in older
fetuses they are located in the
scrotum but in younger
fetuses they may be found
anywhere between the
scrotum and the kidneys. The
testes are the primary male
sex organs or gonads.
6. Penis, (males) find the
bladder, trace this posteriorly
to the urethra. This tube-like
structure curves anteriorly and enters into the penis. The penis will join the
urogenital opening.
7. Vas deferens, tube which extends from the dorsal posterior portion of the
testes. Follow the vas deferens to the base of the bladder where it loops over
the ureters and enters the urethra. Used for sperm to travel to the penis.
8. Be sure to spend some time identifying the reproductive parts of someone
else’s pig who has one of the opposite sex from your own.
Name:
Name:
Section 5- Review and Assessment
Now that your pig is fully dissected, trace from beginning to end the
sequence of structures involved in the following processes:





Digestion
Respiration
Reproduction
Urine production and excretion
Blood circulation
Answer the following questions:
1. What is the function of the umbilical cord?
2. What body system is the spleen a part of and what is its function?
3. What is special about the design of the snout?
4. Briefly describe how you can visually tell the difference between a male
and a female fetal pig (not just what parts they have, but how you can
recognize them).
5. What symptoms might a newborn baby exhibit that would suggest the
possibility that its pyloric sphincter is damaged and will not open? Note:
This is not in your book…think it through.
6. What is the function of the urogenital opening?
7. Compare and contrast the human hand with the pig’s hoof.
8. What difference do you note in the hard and soft palate?
9. What are the two major body cavities of the fetal pig called?
10. What structure separates these two cavities?
11. Why are the thyroid and thymus glands needed?
12. Why is it necessary for the epiglottis to close over the glottis (think about
what happens when you accidentally try to breathe and swallow at the same
time)?
13. What is the function of the liver?
14. What system contains the cardioesophageal and pyloric sphincters?
Describe their functions.
15. What role do you think the rugae play in digestion?
16. What are the functions of the small intestine and the large intestine?
17. Why is the mesentery needed? In other words, what would happen if the
mesentery were not present?
18. What is the difference between the trachea and the esophagus?
19. What function does the pericardial sac serve?
20. What is the role of the kidneys?
21. Gently palpate your own esophagus and trachea. Which is anterior?
22. In step two of the respiratory system section there is a note that says,
“FORM FOLLOWS FUNCTION.” What, specifically, is that statement
referring two in terms of vacuum cleaner hoses and tracheae?