Fetal
Pig
Dissection
Honors Anatomy & Physiology
2011 – 2012
Lucinda Supernavage
INTRODUCTION
Today, you will dissect a fetal pig. This will count as your final exam score and will be graded based on
the following group and individual criteria:
1. Correctly followed dissection guidelines (take caution dissectors and follow the very thorough
directions outlined in this packet). It is the very important job of the reader to make certain the
dissector(s) know exactly how and what to cut. (15 points – group)
2. Correct identification of all bolded instructions in this lab. (35 points – group)
3. The writer is responsible for jotting all notes needed for completion of the lab sheet and calling
the teacher’s attention for pointing out structures needed for a grade…see checklist. (15 points –
group)
4. Participation and proper clean-up (15 points – individual)
5. Lab Analysis – these lab sheets will be given out after clean up (20 points – individual)
6. ALWAYS RESPECT LIFE!!! (all points)
The fetal pig (Sus scrofa) belongs to the following classification taxa:
 domain Eukarya
 kingdom Animalia
 phylum Chordata
 class mammalia
 order Artiodactyla
 genus Sus
 species scrofa
It is an excellent specimen for mammalian dissection because of its convenient size. Along with frogs and
earthworms, fetal pigs are among the most common animals used in classroom dissection. There are
several reasons for this, the biggest being that pigs, like humans, are mammals. Shared traits include
common hair, mammary glands, live birth, similar organ systems, metabolic levels, and basic body form.
Secondly, fetal pigs are easy to obtain because they are by-products of the pork industry. Fetal pigs are
the unborn piglets of sows that were killed by the meat packing industry. These pigs are not bred and
killed for this purpose, but are extracted from the deceased sow’s uterus. Fetal pigs not used in classroom
dissections are often used in fertilizer or simply discarded. Thirdly, fetal pigs are cheap.
AGE: The approximate age (time since conception) of your pig can be determined by the length of your
specimen. Total gestation for a pig is about 114 days while human gestation lasts about 270 days. Use
both charts below to determine and record your pig’s approximate age now. The reader should simply
jot a note in the margin of the lab until you all get your lab sheet.
Please be ready to prove the age of your pig to your teacher when asked.
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40 mm = 54 days
80 mm = 68 days
100 mm = 75 days
158 mm = 86 days
220 mm = 100 days
300 mm = 114 days
• 6 – 8 inches = 75 days
• 8 – 10 inches = 100 days
• 11 – 12 inches + = 115 days
Please review with each other the anatomical terms on the next page before you begin so that you are
able to understand the rest of the lab better.
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Cranial – toward the head
Caudal – toward the rear
Dorsal – toward the back
Ventral – toward the belly
Proximal – near to
Distal – away from
EXTERNAL FEATURES
 Pinna – the flap-like external ear
 Nares – the two nostrils
 Eye – Note the upper and lower
eyelids.
 Look closely in the corner
of an eye and find the small
nictitating membrane (from
Latin nictare, to blink). This
translucent third eyelid can
be drawn across the eye for
protection and additional
moistening while
maintaining visibility.
 In humans, the plica
semilunaris is thought to be
the vestigial remnant of a
nictitating membrane.
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Anus – the terminal opening of the digestive tract where feces are expelled, located just ventral to
the tail.
Urogenital opening – an opening through which liquid wastes and reproductive cells pass. In the
male fetus, this is located just caudal from the umbilical cord. You should also find the scrotal sac
which is a swelling proximal to the umbilical cord. In females, the urogenital opening is just
ventral to the anus.
Mammary Papillae – found on the ventral surface on either side of the umbilical cord in both
sexes. These develop into teats on mature females for nursing their young.
INITIAL GENDER DETERMINATION: Determine the sex of your pig by locating the urogenital opening.
The reader should simply jot a note in the margin of the lab until you get your lab sheet. You will be
able to verify the sex of your pig once you have opened up your specimen.
Please be ready to prove this to your teacher when asked.
PREPARATION
Tie one front leg of the animal with a string that passes
underneath the dissecting pan to the other leg. Repeat this
with the back leg. See the picture on the right. As you cut,
pin your body flaps as needed.
Insert one blade of scissors through the body wall on one side of the umbilical cord and cut posteriorly
to the base of the leg as shown in the picture below.
Continue cutting from the anterior point of this cut so that it
resembles an upside-down U. Your finished cut will be
anterior to the navel and along each side of the navel. The
flap of body wall that contains the navel can be folded
posteriorly to reveal the internal organs of the abdomen as
shown in the picture to the right.
Extend a single cut along the midline of the ventral surface of
the animal to about 2 centimeters from the chin. Cut
completely through the body wall in the abdominal area but
keep the cut shallow in the neck region. See the picture on
the right.
A cut is made on the side of the animal from the point just
posterior to the diaphragm dorsally. A similar cut is made on
the other side. These two cuts will enable you to spread open
the abdominal cavity. See the picture below.
MOUTH & NECK REGION
Use a scalpel to cut the sides of the mouth so that the bottom jaw can be opened for easier viewing. You
will need to cut through the musculature and the joint that holds the lower jaw to the skull.
Open the jaw wide enough so that the glottis and epiglottis are exposed. The epiglottis projects up
through the soft palate into a region called the nasopharynx. The tongue is the most obvious feature in
the mouth. It functions as a taste organ and as a muscular appendage to manipulate food in the mouth.
The hard palate is a bony structure on the roof of the mouth that separates the oral and nasal cavities.
The soft palate is also found on the mouth roof just caudal from the hard palate and is composed of
tissue with no underlying bone or cartilage. While breathing, air passes through the nasal passages to the
pharynx. The pharynx is the space in the posterior portion of the mouth that both food and air pass
through. From the pharynx, it passes through the glottis to the trachea.
Identify the hard palate, soft palate, glottis,
epiglottis and tongue and prove to your teacher.
Use the above diagram of the fetal pig’s internal anatomy and the following text to identify the
underlined structures in your specimen.
Carefully, peel the skin away from the incision in the neck region using a blunt probe (a needle or the
point of scissors will do if a blunt probe is not available). Use the probe to peel away muscle tissue until
the thymus gland on each side of the trachea is exposed. The thymus gland is a grayish mass that covers
the upper trachea and heart. It produces hormones important in the production of plasma cells. The
thymus will decrease in size and function as the pig matures.
Use a probe to separate the two lobes of the thymus gland and to further separate the musculature over
the trachea. The thyroid gland is darker and rounded and lies between the posterior ends of the two
lobes of the thymus gland.
Continue separating the tissue with a probe until the trachea and esophagus are exposed. The esophagus
is dorsal to the trachea. At the point just caudal from the oral cavity is a large hard structure/swelling
attached to the trachea: the larynx or voice box which contains the vocal chords.
Identify the thymus gland, thyroid gland,
trachea, esophagus and larynx and prove to your teacher.
RESPIRATORY SYSTEM
Observe how the diaphragm attaches to the body wall and separates the abdominal cavity from the lung
(pleural) and heart (pericardial) cavities. Contraction of the diaphragm forces air into the lungs.
Follow the trachea to where it branches into two bronchi and observe that each bronchus leads to a lung.
The lungs themselves are reddish and spongy in texture. The left lung contains three lobes and the right
lung contains four. Each lung is located in a body cavity called a pleural cavity.
Identify the diaphragm, the heart, the two main bronchi
and the lungs and prove to your teacher.
CIRCULATORY SYSTEM
The pulmonary artery is capable of delivering a large amount of blood to the lungs but the lungs are not
needed to oxygenate the blood of a fetus, so most of the blood is diverted to the aorta. The diagram
shows that the ductus arteriosus connects the pulmonary artery to the aorta and diverts blood that would
otherwise go to the lungs. Shortly after birth, the ductus arteriosus closes and blood in the pulmonary
artery goes to the lungs instead of the body.
Blood passes from the left ventricle through the aortic arch and aorta to the body. The first branch of the
aorta is the brachiocephalic artery. The second branch is the left subclavian artery which goes to the left
front leg. The right subvclavian carries blood to the right front leg and the carotids carry blood to the
head.
The pericardium is a membrane that surrounds the heart and lines the pericardial cavity. It contains a
lubricating fluid and isolates the heart from body movements such as the expansion and contraction of
the nearby pleural (lung) cavity.
To view details of the aortic arch, ductus arteriosus, and pulmonary artery, it will be helpful to remove
the pig’s left lung. With the left lung removed, the heart can be pushed to the right side to reveal the
aorta and other blood vessels shown in the diagram.
Identify the heart, the aorta, the ductus ateriosus
and the pulmonary artery and prove to your teacher.
DIGESTIVE SYSTEM
The organs you have been reading about and identifying are within the thoracic cavity and above. This
cavity is divided from the abdominal cavity by different membranes and the diaphragm. The esophagus
is a muscular tube dorsal to the trachea which conducts food from the mouth to the stomach. The aorta
and caudal vena cava pass through the diaphragm and the membranes. The following are the digestive
organs of the abdominal cavity.
 Liver – located just caudal from the diaphragm; brown, lobed organ; purifies blood, stores sugar
and produces bile.
 Lift the right lobe of the liver and find the gallbladder. This structure stores bile produced by the
liver. It is connected to the liver via the bile duct.
 It drains into the small intestine by the cystic duct.
 The stomach is located under the left lobe of the liver. It breaks down food and empties into the
small intestine through the pyloric valve.
 The small intestine is highly coiled and receives food from the stomach. It mixes it up with
digestive enzymes for further breakdown and absorption into the blood stream via internal villi.
 The small intestine is broken down into two parts: the duodenum (the straight part) and the ileum
(curly part)
 The pancreas is located dorsal and posterior to the stomach. It extends along the length of the
stomach from the left side of the body (your right) to the point where the stomach joins the small
intestine. It produces many enzymes needed by the small intestine. These enzymes enter the small
intestine by the pancreatic duct. Lift the stomach and identify this light-colored grayish organ.
 The spleen is an elongated, flattened, brownish organ that extends along the posterior part of the
stomach ventral to (above) the pancreas. This organ is not part of the digestive system but it is
advantageous to study it now. The spleen stores and produces red blood cells and certain
lymphocytes.
 The large intestine can be found by following the length of the small intestine. It is a much larger,
tube-like organ, also called the colon. The colon has two functions: the absorption of water and
elimination of wastes.
 The cecum is a blind pouch where the small intestine joins the large intestine. It houses bacteria
used to digest plant materials such as cellulose. The cecum is large in herbivores but much of it has
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been lost during evolution in humans. The appendix in humans is the evolutionary remains of a
larger cecum in human ancestors.
Rectum – can be found at the terminal end of the large intestine. It is storage area for feces (solid
waste). The feces exit the body through the anus.
Urinary bladder – enlarged sac to store urine.
Identify the liver, gallbladder, stomach, small intestines, large intestines, pancreas,
spleen, cecum and rectum and prove to your teacher.
THE UROGENITAL SYSTEM
After the digestive system has been viewed and checked with the teacher, it may be dissected out so that
the urogenital systems can be easily studied. Cut through the junction of the esophagus and the stomach.
Cut away membranes that hold the stomach, liver, pancreas, large and small intestines. Leave an inch or
so of the rectum. Put the specimen pieces aside. Depending on the sex of your specimen, use the
diagrams below to identify the following underlined structures.
The kidneys are located on the dorsal body wall on either side of the midline just below the liver. They
generally help the body eliminate wastes from the blood stream and excess water. They also aid the
body in balancing its ion concentration.
Ureters are tubes which carry urine from the kidney to the bladder which stores the urine prior to
elimination. It is a long tube-like organ located in the posterior region of the abdominal cavity. Urine is
expelled from the body through the urogenital opening which is connected to the bladder by a tube
called the urethra.
If your pig is FEMALE
You will see ovaries that are located on either side of the mid-line just
below the kidneys. This is the organ that produces the eggs. Oviducts
(fallopian tubes) connect each ovary to the uterus at a junction called the
Uterine Horn. Eggs travel down the oviducts once they are released from
the ovaries via a current in the body cavity fluid caused by the beating of
cilia.
Pigs develop in a bicornuate uterus, which means that the uterus possesses
two horns, and is not merely a singular hollow organ, but rather more like
two hollow organs that are fused into a “y” shape. Animals possessing a
bicornuate uterus are able to bear more young since there are more places
for fertilized eggs to attach. Each sow has anywhere from 7 to 12 piglets in a
litter. Like you, the pig is a placental mammal. Placental mammals are
mammals whose fetuses are attached to the mother’s uterus by a placenta,
which provides food and oxygen to the developing baby through the
umbilical cord. Placental mammals make up almost all mammals. Other
mammals, such as kangaroos and echidnas (spiny anteaters) are not
placental.
The vagina is a muscular tube dorsal to the urethra which serves as a passageway for sperm to fertilize
eggs and the exit of embryos during birth.
If your pig is MALE
You will see different structures. Early in the development of the pig (as in all mammals) the testes
are found directly within the abdominal cavity. Later, the testes descend into a sac-like structure called
the scrotum. As the testes descent into the scrotum, they carry along nerves, blood vessels and ducts.
The openings that remain between the abdominal cavity and the scrotal sac are called the inguinal canals.
Cut open one side of the scrotum. Inside you will notice a rather round, whitish structure. This is the
testis. The testes are the sites of sperm and male sex hormone production. On either side of the testis is a
small highly coiled tubule (the epididymis) which stores sperm cells. The epididymis continues as the
ductus deferens which connects to the urethra (which remember connects the bladder to the urogenital
opening). At this junction there are the seminal vesicles and in between these, the prostate gland. If
you follow the urethra caudally you will find the bulbourethral glands. All of these glands secrete fluids
that along with sperm form semen.
OPTIONAL: If the urethra is followed further long, it will be seen to enter the penis. In order to expose
this part of the reproductive system, the pelvic bone and muscles must be cut through mid-ventrally.
Follow the penis to its distal end and note the slight swelling called the glans penis.
Identify the kidneys, ureters, bladder, urethra, female structures (ovaries, oviducts,
uterus and vagina) OR male structures (scrotum, testis, epididymis and ductus
deferens) and prove to your teacher.
OPTIONAL: THE NERVOUS SYSTEM
Dissecting the spinal cord
Remove the tissue that surrounds the vertebrae from the base of the skull caudally to the pelvic girdle.
Avoid cutting any nerves which come out of the column. When the spine has been exposed, carefully
shave off the neural arches of the vertebrae with a sharp scalpel. This will gradually expose the spinal
cord. Look for paired spinal nerves emerging from the cord at regular intervals. Follow one of these
nerves distally to a swelling. This is the dorsal root ganglion which conveys nerve impulses TO the spinal
cord. The nerve coming out of the cord ventral to dorsal nerve is the ventral root which carries motor
impulses FROM the cord.
The brain
Remove the skin and tissue from the dorsal half of the head until the skull is exposed. Cut the occipital
bone away gradually working your way to the cranial tip of the skull. What you will be doing is
carefully chipping the skull away and removing bits of bone. Work until the entire brain has been
exposed. The brain is covered by three membranes or meninges. The outermost layer, the Dura Mater,
is a hard-fibrous connective tissue layer. The Arachnoid (the middle membrane) is a delicate net-like
membrane which is hard to see. The innermost membrane, the Pia Mater, is a very delicate, highlyvacularized tissue which closely follows the contours of the cerebral cortex.
Because the fetal brain is so soft, it is hard to dissect the entire brain out. What can be seen however is
outlined below and in the diagram on the next page.
 Cerebral hemispheres – the two highly convoluted lobes which occupy most of the dorsal brain.
 Cerebellum – this smaller single mass is located caudally. This mass is also highly convoluted.
 Medulla Oblongata – The enlarged base of the spinal cord before it enters the brain.
 Longitudinal Fissure – a deep groove which separates the two hemispheres of the brain.
CLEAN UP DUTIES & ANALYSIS:
 Properly dispose of entire specimen and any pieces that were removed.
 Thoroughly wash tray, dissecting pan and mat using soap and water. Please blot dry.
 Thoroughly wash all dissecting instruments with soap and water. Dry with paper towels.
 Clean lab area using spray solution and disposable towel. Wipe down entire table and all chairs.
Dispose of towel in garbage bag.
 Wipe down aprons with damp paper towels and hang up to dry.
 Dispose of gloves in garbage bag.
 Clean up and inspect lab area before teacher check-out.
Please ask your teacher to check out your lab area. You may only have your lab
sheets for final questions and grades when you are completely cleaned up. Work
on these lab sheets together as a group and hand in when complete!
PIG DISSSECTION TEACHER CHECKLIST
GROUP MEMBERS: ______________________________________________________________________
1. Age _________
25. Pancreas _________
2. Anatomical Terms _________
26. Spleen _________
3. Gender _________
27. Cecum _________
4. Hard and Soft Palate _________
28. Rectum _________
5. Glottis _________
29. Kidneys _________
6. Epiglottis _________
7. Tongue _________
8. Thymus Gland _________
9. Thyroid Gland _________
10. Trachea _________
11. Esophagus _________
12. Larynx _________
13. Diaphragm _________
30. Ureters _________
31. Bladder _________
32. Urethra _________
33 - 36. Reproductive
Female Structures: Ovary _________
Oviducts _________
Uterus _________
Vagina _________
Male Structures: Scrotum _________
14. Heart _________
Testis _________
15. Bronchi _________
Epididymis _________
16. Lungs _________
Ductus Deferens _________
17. Aorta _________
18. Ductus Arteriosus _________
TOTAL SCORE = __________________
19. Pulmonary Artery _________
20. Liver _________
DISSECTION SCORE = _____________
21. Gallbladder _________
22. Stomach _________
PROFESSIONAL? __________________
23. Small Intestines _________
24. Large Intestines _________
CLEAN UP? _______________________
NOTES
Name _____________________________________________________
FETAL PIG DISSECTION LAB SHEET
Approximate age __________________
Honors Anatomy & Physiology
Total Lab Score
Gender __________________
What is the scientific name of the pig? ______________________________________
How are pigs similar to humans?
Compare a human’s gestation to a pig’s gestation.
What is the function of the nictitating membrane? Do humans have this?
What is the urogenital opening? Differentiate between the male’s versus the female’s.
What are teats? Do all pigs have them? ________________________________________________________________
The esophagus is ____________________________ to the trachea which means _______________________________
What is the thymus (NOT THYROID) gland? Is it lateral or medial to the trachea?
The larynx contains what? ____________________________________
The diaphragm separates what cavities? ________________________________________________________________
The left lung contains ____ lobes while the right lung contains ____ lobes.
Oxygenated blood comes from the lungs and enters what side of the heart? ________________
The heart pumps this oxygenated blood through what? ________________ to where? ___________________
What artery takes blood back to the lungs to pick up more oxygen and drop off wastes?
Why do you think the lungs are not needed in a fetal pig to oxygenate its blood?
What diverts the blood to the aorta instead of entering the pulmonary artery and going to the lungs?
What structures have these functions?
1. Storage area for feces ________________________
2. Supplies blood to the head ________________________
3. Stores bile ________________________
4. Stores blood ________________________
5. Membrane over the heart ________________________
6. Colon; absorbs water into the bloodstream and eliminates waste ________________________
7. Purifies blood, stores sugar and produces bile ________________________
8. Used to make noises ________________________
9. Returns blood the heart ________________________
10. Main absorption of nutrients into bloodstream occurs here ________________________
11. Produces many enzymes needed for digestion ________________________
12. Very large in herbivores; has become vestigial in humans ________________________
13. Connects the liver and gallbladder ________________________
14. Lower heart chambers ________________________
15. Conducts food from mouth to stomach ________________________
How do enzymes get from the pancreas to the small intestine? ____________________________________________
What is the function of the cecum? ___________________________________________________________________
What is the function of the spleen? ___________________________________________________________________
What is a bicornuate uterus?
Label the numbered structures:
Which #s is/are the:
 Aorta? _____
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Carotid Arteries? _____
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Two atria? _____
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Ventricle? _____
What was your favorite part of this lab? Which organ/structure did you think was the coolest?!