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Anatomy of the Fetal Pig: Part I
INTRODUCTION
This lab provides students an opportunity to learn various dissecting techniques and to become familiar with
mammalian anatomy. Pig gestation lasts about 17 weeks, and the pigs you will dissect are about 13-15
weeks old.
The fetuses you will use in the following weeks were salvaged from pregnant sows being
slaughtered for food. They are not raised specifically for dissection purposes. The fetuses are
removed from the sow and embalmed with a preservative, which is injected through the umbilicus.
Following this, the arterial and venous systems are injected under pressure with latex, a rubber-like
compound. Arteries (red) are injected through the umbilicus; veins (blue) are injected through one
of the jugular veins at the base of the throat.
With the possible exception of the abdominal cavity, organs rarely appear as they are presented in
a diagram. If the purpose of this exercise were simply to have you memorize diagrams (or
computer screens), we would do only that and bypass the expense, time, and controversy of
dissecting! Dissection is a powerful teaching method, especially for concrete thinkers and visual
learners. Only by dissecting can you really appreciate the structural and functional role of the many
membranes, mesenteries, and connective tissues that will impede your progress every step of the
way. Only by dissecting can you really appreciate the relationship between an organ's texture,
location, and function. I do not take the life (or death) of your pig specimen lightly – this is why I
demand that you take your dissection seriously and utilize your pig to the fullest extent possible.
During these exercises, keep several points in mind. First, be aware that "to dissect" does not mean "to cut
up," but rather "to expose to view." Actual cutting should be kept to a minimum. Tissues are picked and
teased apart with needle probes, forceps, and blunt probes in order to trace the pathways of blood vessels,
nerves, muscles, and other structures. Never cut or move more than is necessary to expose a given
part. Second, pay particular attention to the spatial relationships of organs, glands, and other structures as
you expose them. Realize that their positions are not random. Third, we encourage you to engage in
collaborative discussions with your classmates and compare dissections.
Be sure to read all instructions before beginning the dissection. I have also provided you with a
photographic reference book. Be careful not to cut structures that you will need in later dissection labs (like
blood vessels). You do not need a scalpel for this dissection. The pig skin and muscle tissue are very supple
and can be easily cut with scissors. Using scissors will also prevent unwanted damage to the pig.
There are reflection questions scattered throughout this lab procedure. Make sure you figure out the
answers to these questions before moving on to the next section. All are fair game for the test. When
dissecting, use the dissection book as a guide and for further info as needed.
SAFETY AND HYGIENE
1. Practice safe hygiene when dissecting. Do not place your hands near your mouth or eyes while handling
preserved specimens. Although most of the preservatives in use today are non-toxic to the skin, they may
cause minor skin irritation. If the preservative gets on your skin, wash with soap and warm water.
2. If the preservative gets in your eyes, rinse them thoroughly with the safety eyewash.
3. If you choose to, wear lab gloves, we will reuse them for a total of 3 days. A variety of glove sizes are
available. These gloves are expensive--please don't waste them. You may opt out of using gloves.
4. Work in pairs to complete the dissection. One person should read the instructions while the other person
dissects the pig. Both students should read the entire lab before any cuts are made!
5. After bagging your pig and placing it in the refrigerator, wash your tray and utensils; stacking them neatly
by the sink. Wipe up your station.
PROCEDURE
Pigs are mammals. Mammals have mammary glands, hair, and occur in two sexes. Their genitals or
reproductive organs distinguish the sexes.
Pigs, like humans, are placental mammals, meaning that development occurs inside the uterus of the mother.
The umbilical cord stretches between the developing animal and the placenta. The placenta is a blood rich
lining of the uterus where gas exchange occurs and nutrients are acquired. Pigs and humans are tetrapods
because they have four limbs. Pigs walk on all four limbs; their toenails serve as hooves.
External Anatomy
1) Place the pig in a dissecting tray. Obtain 2 pieces of string from Mrs. Leider. Tie one end of one piece of
string to the right front hoof, put the string under the pan, and tie to the left front hoof. Then, tie the back legs
in similar fashion. Determine the following anatomical landmarks of your specimen.
 dorsal: toward the back of the body
 right and left: the pig's right and left, not
yours!
 ventral: toward the underside of the body

proximal: closer to the trunk
 anterior (cranial): toward the head end of
the body
 distal: farther from the trunk
 posterior (caudal): toward the tail end of the
 superficial: lying closer to the body surface
body
 deep: lying under or below
 lateral: to the side of the body
 median: toward the center of the body
2) Note the following body regions: head, neck, trunk, appendages, and tail
3) Examine the limbs, and determine which parts are homologous to your limbs.
4) Locate the umbilical cord arising from the ventral portion of the abdomen.
5) Locate the nipples, which are part of the mammary glands. Nipples are not an indication of sex.
6) Notice any hair on your pig. Write down where it is found.
Hair is located throughout the body of the pig but is concentrated around the eyes,
nose, and mouth.
7) Locate the anus under the tail.
8) In females, locate the urogenital opening just anterior to the anus and a small, fleshy urogenital papilla
projecting over the opening.
9) In males, the urogenital opening is located just posterior to the umbilical cord. The duct leading to it runs
forward in the penis, which can be felt under the skin. The genital system and urinary system are joined in
males.
10) Be sure you can identify pigs of both sexes. Travel to other lab stations as necessary.
Reflection questions:
A. Ungulates (hooved animals) like the pig walk with the
weight of the body borne on the tips of the digits
(unguligrade locomotion). Cats and dogs use digitigrade
locomotion (walking on the balls of their feet). Humans
typically use the entire foot for walking (plantigrade
locomotion). What form of locomotion do you use when you
sprint?
Sprinters run only on the balls of their feel =
digitigrade locomotion
B. Although male mammals have nipples, as a general rule
they do not lactate. Why is male lactation the exception
rather than the rule? (HINT: there are very few monogamous
mammals)
Since males rarely take care of their own young, it is not
necessary for them to lactate and supporting mammary
glands would not be beneficial.
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Skinning the pig (page 22 in the Dissection book)
11) Make a mid-ventral incision in the skin from the jaw to the umbilical cord. Be careful to cut the skin only,
not the underlying delicate muscle tissue. Do NOT remove the skin from the head (face or skull).
12) Cut around the umbilical cord and proceed posteriorly to a point just anterior to the external genitalia.
13) As you cut, lift the skin with your finger and separate it from the underlying muscles. Separate the fascia
(the white connective tissue) as you loosen the skin; sliding your forefinger between skin and muscle.
14) Continue to retract the skin toward the dorsal side.
15) Cut along the medial surface of the forelimbs and hind limbs and extend the cut to the wrist/ankle.
16) Leave skin intact around the urogenital and anal areas (perineum). Remove the skin from the proximal
1/3 of the tail.
17) Turn your pig over. Complete the skinning of the limbs and the entire dorsal surface from the base of the
skull, the neck, dorsal thorax and abdomen, to the proximal 1/3 of the tail. Do not discard the skin. Use it to
wrap the pig, in addition to damp paper towels, at the end of each dissection. The only areas still covered by
skin are the head, feet, perineum, and the distal portion of the tail.
Musculature (pg 26 – 28)
18) Once your pig is skinned, the muscles are easily visible. You will be expected to know where the
following muscles are and to be able to identify them on a lab practical exam:
a. Latissimus Dorsi
d. External Oblique
b. Trapezius
e. Achilles tendon
c. Pectoralis Major
f. Masseter
Salivary Glands (pg 51)
There are three pairs of salivary glands, the parotid, mandibular and sublingual.
19) Carefully remove the muscle layer from one side of the face and neck to expose a large, rather dark
triangular gland, the parotid. The differentiation between muscle tissue and glandular tissue is the presence
of fibers in muscle, whereas the parotid gland has the appearance of being composed of many small nodules.
The parotid lies just ventral to the base of the ear and extends to the caudal border of the masseter muscle.
(It is difficult to isolate so be very careful!)
The mandibular gland is large and somewhat lobed. It is located just caudal to the masseter muscle and
partially covered by the cranial portion of the parotid. You will cut through the parotid to expose the
mandibular.
The parotid gland secretes a watery fluid, the mandibular and sublingual glands a more viscous fluid. These
secretions function in maintaining the mucous membranes in the mouth and pharynx in a moist condition and
in lubricating food for ease in swallowing. In addition, the glands produce enzymes which initiate
carbohydrate digestion by reducing starch to maltose and glucose.
Oral Cavity (pg 54)
20) Insert a sturdy pair of scissors into one corner of the mouth, and cut posteriorly for 5 cm. Repeat this on
the opposite side. It will not be necessary to use the bone shears, but see Mrs. Leider if you are having
significant difficulties opening up the mouth.
21) Stretch the mouth with your hands, and create an angle of 180 degrees of the jaws so that the mouth
stays open.
22) Locate any teeth that may be present. Feel the gum line to locate embryonic teeth. Like all young
mammals, fetal pigs have milk teeth (baby teeth) that are later replaced by permanent teeth.
23) View the tongue which helps swallow food. Note the papillae on the tongue. These provide friction for
food handling and contain taste buds.
24) The hard palate separates the nasal passage from the oral cavity. It is found at the front of the mouth and
contains several ridges. Just posterior to the hard palate is the smooth soft palate. The uvula is an extension
of the hard palate, which hangs down in the back of the throat in humans.
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Pharynx (pg 54)
25) Push down on the tongue until you see a pointed flap of tissue in the back of the throat pointing upwards.
This is the epiglottis that covers the glottis. The glottis leads to the trachea (windpipe).
26) Insert the blunt probe into the glottis where it enters the trachea. Then place the probe in the esophagus,
which lies dorsal to the trachea.
27) Make a midline cut in the soft palate from the epiglottis to the hard palate. Then, make two lateral cuts at
the edge of the hard palate.
28) The space you create will expose the nasopharynx. (don’t be alarmed when you see “nothing”. You are
simply connecting the mouth to the nose.
Reflection question:
C. Why is the pharynx called the “crossroads of food and air”?
The pharynx is where food moves
into the esophagus and air moves
into the trachea. The epiglottis,
located in the pharynx, is what
covers the trachea when
swallowing and prevents food and
air from entering the correct tube.
Thoracic and Abdominal
Incisions(pg 61-64)
29) Always make incisions with the
scissors pointing up, not down. Incision
directions are numbered on Fig 4.
30) Cut anteriorly from the
diaphragm until you reach the throat.
31) Make a longitudinal cut from the
diaphragm region to the umbilical cord. Be
careful to cut only muscle.
32) Cut around the umbilical cord, and cut
posteriorly left and right of the cord so that
a flap is formed.
33) Make three sets of lateral cuts.
The first should be made anterior to the
front limbs. Dispose of any excess fluid
down the sink.
34) The second lateral set of cuts should
be made just posterior to the forelimbs.
The last set of lateral cuts should be made
just anterior to the hind limbs. Cut deep
enough so that you can fully view the
contents of the abdominal and thoracic
cavities.
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30
31
34
32
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35) Carefully remove any excess latex. To free the umbilicus, cut through the umbilical vein approximately 1
cm from where it enters the liver. Do not cut off this flap--it contains important organs that we will examine
later!! Hold back the flaps of your pig so that you can see the entire abdomen/thoracic cavity.
Neck Region (pg 70)
In the neck region, locate the larynx. The larynx is the voice box and sits on top of the trachea or windpipe.
The thymus gland is part of the immune system. It is a V ‐shaped gland found just below the larynx.
Immediately beneath the thymus in the neck is the thyroid gland, a small, solid, reddish, oval mass. The
thyroid secretes thyroxine, which in mammals influences the metabolic rate of cells, which in turn influences
growth and development. Because iodine is necessary for the production of thyroxine, table salt is often
iodized. If synthesis of thyroxine declines (e.g. due to a lack of iodine), the anterior pituitary increases the
release of thyroid stimulating hormone (TSH). This may stimulate the proliferation of thyroid cells, but if there
is no iodine, thyroxine production will not increase, which causes additional TSH release. The thyroid also
produces calcitonin, a hormone that stimulates osteoblasts to lay down bone. The consequence of this
activity is a surprisingly rapid decline in blood calcium levels. If blood Ca levels drop too low, or if extra Ca is
needed, the parathyroid glands release PTH. The parathyroid is not a discrete organ in mammals –
parathyroid tissue is embedded in the thyroid. PTH raises blood Ca levels by activating osteoclasts, by
stimulating Ca reabsorption in the kidney, and by activating vitamin D to enhance absorption of Ca from food.
Reflection question:
Describe the role that the thyroid plays in bone growth.
The thyroid produces calcitonin, which stimulates osteoblasts to lay down bone.
Thoracic Cavity (pg 70)
The body cavity of mammals can be divided into
the thoracic cavity and the abdominal cavity.
The thoracic cavity contains the heart and lungs.
Fold back the flaps covering the chest wall.
Remove the membranes that divide the thoracic
cavity into three parts: the left pleural cavity
containing the left lung, the right pleural cavity
containing the right lung, and the pericardial
cavity containing the heart.
Examine the lungs. Locate the four lobes of the
right lung and the three lobes of the left lung.
Locate the bold printed terms on your specimen.
Use Figure 5 as a guide.
36) In the neck find the trachea and use it as a
landmark to locate the esophagus. Make a
small incision in the esophagus in the throat
and insert a blunt probe anteriorly; note
where it emerges in the oral cavity.
Abdominal Cavity (pg 63 – 64)
A membrane called the peritoneum lines the
abdominal cavity. The peritoneum consists of
epithelial tissue supported by connective tissue.
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Some sheets of peritoneum called mesenteries project from the abdominal wall and support the organs. The
large, brown, organ that snuggly fits under the diaphragm is the liver. It has many vital functions including
making bile, storing glycogen, and maintaining blood glucose levels.
The gall bladder stores and releases bile. Bile aids in the digestion of fat. The gall bladder sends bile to the
duodenum through the bile duct. The gall bladder can be found on the dorsal side of the right lobe of the liver.
It will appear greenish. Locate the bile duct as it leaves the gall bladder.
The pancreas secretes pancreatic juices, which enter the duodenum through the pancreatic duct. These
secretions aid in the digestion of proteins, fats, and carbohydrates. The pancreas also secretes insulin and
glucagon into the bloodstream to maintain normal blood sugar levels. The pancreas can be found under the
stomach in the mesentery that joins the stomach and small intestine.
The spleen is a part of the immune system and stores red and white blood cells. It can be found attached by
mesentery to the stomach and is a long, reddish organ.
Return to the abdomen, and locate the stomach, duodenum, and large intestine. Note where each organ ends
and the other begins. Use Figure 5 as a guide.
37) Insert the blunt probe through the incision made in #36 posteriorly toward the stomach (you will need to
move the liver to one side to fully expose the stomach). Note that the esophagus penetrates the
diaphragm before entering the stomach.
38) Cut open the stomach lengthwise with your scissors. The contents of a fetus's digestive tract is called
meconium, composed of a variety of substances including bile stained mucus, amniotic fluid, sloughed
epithelial cells, and hair. Clean out the stomach and note the folds (rugae).
Reflection question:
D. You learned about the rugae in Biology. These are folds within the walls of the
stomach muscle. What function do the rugae play?
Then rugae allow the stomach to expand or contract greatly when needed without
putting pressure on the stomach. This can be very important so that animals can
eat/drink a large amount when food is plentiful.
Many glands that secrete pepsinogen and hydrochloric acid are embedded in the wall of the stomach. Two
smooth muscles, the cardiac and pyloric sphincters, control the movement of food through the stomach.
The majority of digestion and absorption takes place in the small intestine. It is composed of the
duodenum, the jejunum, and the ileum, the latter two being difficult to distinguish. The duodenum, into which
bile and enzymes from the gall bladder and pancreas enter, passes posteriorly and then curves to the left.
The coils of the small intestine are held together by mesenteries. A rule of thumb is that the small intestine in
both pigs and humans (omnivores) is about five times the length of the body. Note the lymph nodes
embedded in the mesenteries. These nodes filter pathogens from the lymph.
39) Locate the caecum, a small blind-ended sac found at the juncture of the ilium and the colon (large
intestine). This juncture is also the site of the ileocecal valve. Feel for it by rolling the junction between your
index finger and thumb. In the pig, the caecum houses a symbiotic bacterium that helps break down cellulose
(a major component of plants) – much in the same way that gut protozoans in termites allow the termites to
eat wood. Many herbivorous mammals (pigs, horses, rodents, rabbits) use "hindgut fermentation" in the
caecum to digest cellulose. The "ruminants" (camels, giraffes, deer, sheep, and cattle) use "foregut
fermentation".
Ruminants have a multi-chambered stomach in which cellulose breakdown takes place. This breakdown is
aided by their ability to regurgitate the contents of their fermentation chamber back into their mouth for further
mechanical breakdown (i.e., chewing cud). In humans the caecum is known as the appendix and is not used
in digestion. Although the human appendix contains some lymphatic tissue, its function is poorly understood
and it can be removed without any harmful effects. So why haven't we lost our appendix completely? Recent
evidence suggests that the smaller it gets, the more likely it is to get obstructed, inflamed, and infected
(appendicitis). Too large an appendix is wasteful, too small is dangerous. Barring a mutation that eliminates
it completely, we are stuck with a slightly wasteful, occasionally dangerous tradeoff. Evolution is not about
perfection.
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Reflection questions
E. Saliva contains water (to moisten food), mucus (to lubricate food), salivary amylase (to break down
starch), bicarbonate (to buffer acids in food), and antibacterial agents. What role do the a) bicarbonate and b)
the antibacterial agents serve?
a) Bicarbonate
Protects our sensitive organs and tissues (including teeth) from being damaged by
excess acid.
b) Antibacterial agents
Kill bad bacteria in our food so that it does not enter our bodies and make us sick.
F. Everyone knows different parts of the tongue are especially sensitive to different tastes. But why do we
devote tongue space to bitterness? (Wouldn’t it be simpler to NOT taste things that are bitter?)
It is very important to be able to taste bitter substances because they are often
poisonous. In fact, this is one theory of how the taste of bitterness evolved; those
who thought poison tasted bitter and spat it out lived longer and passed on their
genes.
G. In humans, the uvula hangs as a pendant from the posterior end of the soft palate. During swallowing, it
lifts upward and closes off the nasopharynx. Why is this important?
This is very important so that food and other substances do not enter the nasal
cavity, called nasal regurgitation, which can cause nasal irritation and infection.
H. Is diarrhea a defense strategy to rid your body of pathogens or a mechanism intestinal pathogens use to
spread to others (chronic diarrhea is very prevalent in less developed countries with no sewage treatment)?
(explain your answer)
Diarrhea is a defense strategy to get rid of pathogens as quickly as possible before
they enter your system. However, many different pathogens have evolved to take
advantage of this response and use it as means of fast and easy transmission.
I. Early coal miners often suffered from rickets, a disease characterized by brittle bones. Miners rarely see
the sun, a source of vitamin D. Why does Vitamin D deficiency cause brittle bones when it’s Ca that causes
bone to be strong? What is the relationship between Vit D and Calcium?
Vitamin D stimulates the body to absorb more calcium. Without Vitamin D, the
intestines do not absorb enough Ca into the blood, free blood calcium drops, the
parathyroid hormone releases PTH to signal osteoclasts to break down bone in
order to free Ca for the blood. This can then cause brittle bones and even rickets.
J. Carnivores have a shorter intestine than herbivores. Why? (What is it that the herbivores have more of in
their diet that may need additional “processing” time?)
Herbivores eat a large amount of plant tissue which contains large amounts of
cellulose, which is very difficult to break down. Much of this digestion is done by
bacteria through fermentation, which takes a longer time and a longer digestive
tract.
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