Fetal Pig Dissection
Background:
Mammals are vertebrates having hair on their body and mammary glands to nourish their young. The majority are placental mammals in
which the developing young, or fetus, grows inside the female's uterus while attached to a membrane called the placenta. The placenta is the
source of food and oxygen for the fetus, and it also serves to get rid of fetal wastes. The dissection of the fetal pig in the laboratory is important
because pigs and humans have the same level of metabolism and have similar organs and systems. Also, fetal pigs are a byproduct of the pork
food industry so they aren't raised for dissection purposes, and they are relatively inexpensive.
In this lab you will be examining many characteristics of an unborn mammal – the fetal pig. Dissection will help you get a 3-dimensional
picture of how all the systems fit together. You’ve seen separate diagrams of many of the major systems. Now you’ll get to see how they are
arranged spatially. You’ll also get a better idea of the texture of many organs that make up the pig’s system.
This lab will be broken in the following parts:
A – External Anatomy and Oral Cavity
B – Digestive System
C – Circulatory System
D – Respiratory System
E – Urogenital System
F – Nervous System
Objectives:
 To learn the major anatomical directions and sections and use them to describe external and internal structures of the fetal pig.
 To understand the major organ systems of the fetal pig and compare them with those of humans.
 Compare the functions of certain organs in a fetal mammal with those of an adult mammal.
 To understand the fundamental changes involved in the transformation from fetal to adult circulation/respiration.
 To relate the structure (anatomy) of the fetal pig to its function (physiology).
 Identify major structures associated with a fetal pig's digestive, respiratory, circulatory, urogenital, & nervous systems.
Materials:
preserved fetal pig, dissecting pan, dissecting kit, dissecting pins, string/twine, plastic bag, metric ruler, paper towels
Pre-lab:
Make sure to perform ALL PARTS of the Pre Lab (Separate worksheet) before the dissection
General Directions: All underlined words must be located on your pig and all numbered questions must be answered on each of your packets.
Italicized sections are often answers to hand-in questions. Your teacher will check the questions as you work through the laboratories. In the
dissection and observations of the internal organs, you will proceed by systems and remove organs only when directed to do so. Removing
organs early may damage systems to be studied at a later point or make it harder to find them.
Read each section thoroughly and understand what is being asked of you before you start cutting. Study and use the accompanying diagrams to
aid in your observations of the internal organs. Try to find landmarks. Look for something before asking for help! The instructor's job is to
guide and assist you in dissection and identification, not to find everything for you! You may find it helpful to examine the models and any
other dissection manuals or atlases on display. Remember throughout these dissections that left and right orientations refers to the pig's left and
right, not yours. Not all pigs are identical. Aside from the obvious male/female dichotomy any differences in pigmentation and external
anatomy, there may be anomalies ranging from the precise pattern of circulatory vessels to the exact arrangement of muscles. These pigs have
been injected with latex so that arteries appear pink and veins blue.
As you dissect, keep in mind the interrelationships of systems. While concentrating on a single system, use care not to damage other systems.
Dissect carefully and do not mutilate your pig. Use as much blunt dissection as possible, but do not hack around. Again, most cuts can be done
with the scissors. Occasionally, the scalpel must be used. Scissors will often be more useful though. Never wash away tissue down the drain –
simply wrap them in paper towels and discard them in the trash cans where the instructed indicated. Remember to play it safe in the lab: always
handle dissecting instruments with extreme caution, wear latex gloves, apron, and protective eye-wear at all times.
Dissection is an art and you must be as careful as you can during this laboratory. Do not carry any of the sharp dissection tools around the
room.
***Wear your lab apron and eye cover at all times. Watch your time and be sure to clean up all equipment and working area each day
before leaving.
IF YOU DO NOT COMPLETE ALL PARTS IN THE SAME DAY. MAKE SURE TO WRAP PIG WITH PAPER TOWELS AS
INSTRUCTED AND PLACE IT INSIDE THE PLASTIC ZIPLOCK BAG. ALSO MAKE SURE YOUR PIG IS IDENTIFIED SO
YOU CAN FIND IT AND CONTINUE YOUR DISSECTION LATER.
Part A: External Anatomy & Oral Cavity
I.
1.
External Anatomy
Obtain a fetal pig and thoroughly rinse off the excess
preservative by holding it under cold running water.
This will reduce the irritating preservative odor (do
not worry about removing all the preservative).
Although great progress has been made in
preservative technology and some biological supply
houses use new chemicals with no noxious odor, no
preservative is perfect.
Note: It may be beneficial to rinse off your pig again after
making initial incisions (when thoracic and abdominal
cavities are opened). Remember to this carefully so not to
damage or displace internal organs. Also the pig must be
tied down before attempting to do so.
2.
3.
5.
Lay the pig on its side in the dissecting pan
You will be examining several characteristics of an
unborn mammal. Before you begin, acquaint yourself
with (or review) the anatomical directions and planes
of the pig's body-dorsal, ventral, cranial (or
anterior), caudal (or posterior) directions, and
frontal, sagittal, and transverse planes. Two other
helpful descriptives, proximal and distal, relate the
location of one structure to that of another. Proximal
indicates that something is relatively close to another
structure. For instance, your elbow is more proximal to
your shoulder than is your wrist. Distal is the opposite
of proximal and refers to a structure that is farther
away. Your wrist is more distal to your shoulder than
is your elbow. Other relative terms illustrated in are
medial and lateral. Medial refers to the condition of
being located closer to the center of the body. Lateral
describes the condition of being located more to the
side.
A fetal pig has not been born yet, but its approximate
age since conception can be estimated by measuring
its length. The period of gestation for the pig is 112115 days. The age of the fetus can be estimated by
measuring the body length from the tip of the snout to
the attachment of the tail. Compare this length to the
data given on relative sizes of a fetal pig at different
times during gestation or the time of development
inside the uterus. (mm = millimeters)
21 days = 11mm
35 days = 17mm
49 days = 28mm
56 days = 40 mm
100 days = 220 mm
115 days = 300 mm
Measure your pig's length from the tip of its snout to the base of its tail and record this on your hand-in.
6.
Examine the pig’s overall body structure
4.
The pig's trunk is divided into two regions: thorax (chest) and abdomen (stomach).
7.
Study the pig's appendages and examine the pig's toes. Count and record the number of toes and the type of hoof the pig has.
Generally speaking, orders of mammals are recognized rather easily by their external appearance. These external features, which separate
mammals into orders, are such traits as the number of digits (toes or fingers) on the feet, method of walking or other locomotion and
characteristics of the teeth.
The pig is called unguligrade because it walks on its hooves. Humans are plantigrade because we walk on the entire soles of the foot. Dogs and
cats are digitigrade because they walk on their digits. In pigs, the first digit of both the fore and hind limb is absent and the second and fifth
are reduced in size but remain functional.
Pigs are in the mammalian order Artiodactyla, meaning "even-toed," and you can see the two large toes anterior to two small toes on each
foot.
8.
9.
Locate the wrist, elbow, and shoulder of the forelimbs and the ankle, knee, and hip of the hindlimbs.
Examine the pig's head. Locate the eyelids (should be closed in the fetus) and the external ears or pinnae. Also find the external
nostrils (nares on snout). Ventral to the snout is the mouth, normally with the tongue protruding from the opening.
Examine the eyes. They have an upper and lower lid and a small mass of tissue in the upper corner known as the nictitating membrane. This
helps keep the eye clean. Birds can moisten their eyes in flight using this membrane and not blinking; blinking could cause a collision with a
branch or tree.
The lips around the mouth are well developed and the upper lip is usually cleft in the center by a groove called the philtrum. Humans also have
a philtrum. This is the indent underneath your nose. The external nares (nostrils) are found on the nose.
Examine the ears. They have a flexible outer flap called the pinna. The pinna helps the pig hear by focusing the sound.
Many mammals have sensory facial hairs called vibrissae; however, our pigs do not possess these yet. They are evident once a pig reaches
maturity. They help organisms feel their way around in the dark.
10. Locate the umbilical cord midventrally on the trunk. This was connected to a placenta within the uterus of the sow for nutrient/waste
exchange. With scissors, make a transverse cut across the cord about 1 cm from the body. Examine the three openings in the umbilical
cord.
Observe that it contains three blood vessels: a large vein and two smaller arteries. The largest is the umbilical vein, which carries nutrient-rich
blood from the placenta to the fetus. The two smaller openings are the umbilical arteries, which carry waste-rich blood from the fetus to the
placenta.
11. Lift the pig's tail to find the anus. Study the ventral surface of the pig and note the two rolls of tiny bumps called mammary
papillary, or teats (nipples). These are present in both sexes. In the female these structures connect to the mammary glands that
develop later in life.
Mammals have two unique external characteristics, which distinguish them from all other vertebrates: (1) all mammals have hair at some time
during their development, and (2) all female mammals possess mammary glands with external openings for nourishing the young. Your fetal
pig probably does not have a lot of hair due to the fact that it is not fully developed yet. However, at maturity most pigs do have some strands
of hair on their body.
Observe the paired row of nipples on the ventral surface of the abdomen in both sexes. The actual number of nipples varies from mammal to
mammal. Animals that have litters tend to have more nipples.
12. Determine the sex of your pig by locating the urogenital opening through which liquid wastes and reproductive cells pass. In the
male, the opening is on the ventral surface of the pig just posterior to the umbilical cord. The penis is contained in the skin tissue of
the lower abdomen and normally cannot be seen prior to dissection. In the female, the opening is ventral to the anus. This is called a
genital papilla. Record the sex of your pig.
Sex Hints: The penis and urethral opening of the male pig are located just behind the umbilical cord. Ventral to the tail of ta male pig is the
scrotum. If your pig is young, the scrotal sacs may still be empty, as the testes (male gonads) descend just before birth. If you have a more
mature male, the testes will have descended to fill the scrotum. If the pig is female, you will notice a small projection just below her tail. The
opening just below her tail is the anus; the one below the small projection is the vaginal orifice.
Most mammals have separate urogenital and anal openings. In female pigs the urinary and genital openings are also separated. The urethral
opening is the most ventral with the vaginal orifice just behind to it. The anus is located at the base of the tail dorsal to the vaginal orifice. Be
sure to be able to identify both male and female pigs and their reproductive structures.
Locate all three openings (urethral opening, vaginal orifice, and anus) on the female pig. The urethral opening excretes urine and the vaginal
orifice is the opening of the birth canal. In males, the urogenital structures consist of the penis (which has an opening just behind the umbilical
cord)and two saclike swellings called the scrotum, containing the testes. The scrotum lies ventral to the anus. The anus of the male is at the
base of its tail. Locate these two openings: urogenital opening of the penis and the anus. They are just behind to the umbilical cord.
II. Oral Cavity
1.
Carefully lay the pig on one side in your dissecting pan and cut away the skin from the side of the face and upper neck to expose the
masseter muscle that works the jaw, lymph nodes, and salivary glands. Label these on your hand-in. Salivary glands start the
digestive process by producing enzymes that initiate the breakdown of sugars and other basic nutrients. It also helps moisten the food
to facilitate macerating it and transporting it across digestive track.
2.
3.
4.
You will now study the oral cavity (mouth) of the
pig. Inset a pair of pair of scissors in the angle of
the lips and cut deeply on one side of the head
posteriorly through the neck. Cut deeply (3cm)
into both corners of the mouth (see figure 2). This
may be difficult, as you must cut through both
tissue and bone. Be sure to follow the curvature of the throat and do not cut straight back into the neck tissue. Follow the curvature of
the tongue to avoid cutting the roof of the mouth. Your incision should extend posteriorly through the jaw. Hold down the epiglottis
and surrounding tissue and continue your incision dorsal to it and on into the opening of the esophagus. Repeat the same procedure on
the other side so that the lower jaw can be pulled down to expose the structures of the mouth and pharynx as show above. Then apply
gentle pressure to force mouth open and spread the jaws.
Examine the tongue with all its iny projections called sensory papillae (home of microscopic taste buds) These have sensory nerve
cells that detect taste. The papillae are present especially visible near the base and along the anterior margins. Notice that the tongue
is attached posteriorly and free anteriorly.
Observe the ridged roof of the mouth called the hard palate, which is supported by bone and cartilage. The soft palate is the fleshy
portion of the roof of the mouth and lies caudal
to the hard palate.
The anterior part of the palate is the hard palate, while
the posterior part is the soft palate.
1.
2.
3.
4.
Locate the epiglottis, a cone-shaped structure at
the back of the mouth (flap like structure at the
top of the trachea).
Above the epiglottis, find the round opening of
the pharynx. This cavity carries air from the
nostrils to the trachea, a large tube in the
thoracic area, which supplies air to the lungs.
Noticed paired nasal cavities that lie dorsal to
the roof of the mouth, these lead to the
nasopharynx, (space posterior to the nasal
cavities and soft palate)
The far back of the oral cavity is the
oropharynx, which is difficult to visualize because incision cuts through it on each side (posterior extension of nasopharyx).
Together they are referred to as pharynx in general.
5.
Dorsal to the glottis (opening of the trachea) find the opening to the esophagus. The esophageal opening, which is the entrance to the
esophagus (food tube) can also be found in the back of the throat.
In other words, the pharynx splits into the trachea (air) and the esophagus (food/water). The esophagus is located behind the trachea.
Special valves and muscles control which opening is open, depending on whether the animal is swallowing or breathing.
6.
7.
Examine the teeth of the pig. Canine teeth are longer for tearing food.. Incisors are shorter and used for biting. Molars are flat and
wide to facilitate the maceration of food to aid stomach in its digestion. Pigs are omnivores, eating plants and animals.
There should only be a few deciduous teeth already erupted in a fetus. Other teeth are still being formed and may be present as bulges
of the gums. Make an incision in one of these bulges to try to observe the developing tooth.
Mammals generally have two types of teeth - incisors, located in the very front of the oral cavity and cheek teeth located toward the back of the
oral cavity. The canine teeth are modified incisors. The teeth structure is usually adapted to the animal’s diet. For example, carnivores have
stronger incisors and canine teeth, while herbivores have more molars or check teeth.
8.
Label the drawing of the inside of the pig's mouth.
If time remains, continue with Part B: The Digestive System. Otherwise, clean up your materials and work area. Wrap the pig in damp
paper towels and put it in a zip-lock plastic bag. Clean, wash, and sterilize your lab equipment and return it to the supply cart. Sanitize
table tops and wash your hands thoroughly with soap and water.
Part B: Digestive System
I.
1.
2.
3.
Making the Incisions:
Be sure to wear your lab apron and eye cover. Obtain your dissecting equipment and pig from the supply cart.
Place the fetal pig ventral side up in the dissecting tray.
Tie a string securely around a front limb. Run the string under the tray, pull it tight, and tie it to the other front limb. Repeat this
procedure with the hind limbs to hold the legs apart so you can examine internal structures
Be careful not to cut any underlying organs. Always cut away from yourself when using scissors for better control. Rotate the dissecting pan as
necessary for better access Be sure to keep the tips of your scissors pointed upward because a deep cut will destroy the organs below. A good
idea is to make several shallow cuts as oppose to one deep cut.
After you have made your incisions through the body wall, you will see the peritoneum, a thin layer of tissue that lines the body cavity. Cut
through the peritoneum along the incision lines.
Note: When you cut through the thoracic cavity, you will encounter bone. You must cut through this bone to expose the underlying organs.
4.
5.
6.
7.
8.
Using a sharp scalpel, make a small incision through the abdominal skin and muscle about ½-inch above the umbilical cord.
IMPORTANT: Do not use the scalpel for further dissection work today, unless specifically instructed to do so. Use scissors to
continue cutting along the midsagittal line on the ventral surface (INCISION 1), first cutting upward toward the neck (it will
eventually be necessary to cut through the ribs, but the initial cut should only involve the skin)
necessary to cut through the ribs as well).
To find the exact location for the incision marked 2, press along the thorax with your fingers to find the lower edge of the ribs. This is
where you will make incision 2.
Turn the tray around and cut down to the caudal (tail) end of the pelvic region, leaving ½- inch border around the umbilical cord. This
step is important to prevent cutting of the umbilical vein and arteries in the abdominal cavity.
Continue the midsagittal cut down into the pelvic region. Cut around the other side of the umbilical cord (INCISION 2), again
leaving about a ½-inch border. Stop your cut about one inch short of the anus.
Make the two lateral incisions just in front of the hind legs (INCISION 3).
If you have a male pig, cutting off-center ensures that you do not cut the penis, which is incompletely formed in the fetal pig and appears as a
thickened tube within the skin of the lower abdominopelvic area.
9. You may omit INCISION 4.
10. Make two lateral incisions (INCISION 5) through muscle and ribs out from the midline incision. Cut the skin flaps back close to the
backbone so they will remain open. Be careful not to injure the kidneys. Pull back the two flaps of skin
11. Lifting the lateral flaps of ribs, skin and muscle on each side, cut the diaphragm, which is attached to the inside body wall. You should
now be able to peel open the left and right flaps of the ventral body wall like a book.
12. Wash out the cavities of the pig in a sink if needed to remove any brownish material (mainly preservative, bile, and clotted blood)
while being careful to keep the organs in place.
Note: You will need to cut the diaphragm along the sides) and muscle to view the internal organs.
13. Locate the umbilical vein inside the abdomen which extends through the liver. This vein carries in nutrients gathered through the
placenta from the maternal blood. Once determined, cut it and lay back the cord
14. Once the vein is cut, carefully pull the flap of skin, including the end of the umbilical cord between the hind legs. Your are now able
to see the organs of the abdominal cavity.
II. Studying the Digestive System
The digestive system is responsible for the absorption of nutrients from
food. In mammals it is highly specialized with areas dedicated for
1.
2.
3.
4.
Be sure you are wearing your lab apron and eye cover.
Find the most obvious structure in the abdominal cavity, the
brownish-colored liver. It is a multilobed structure under the
lungs and diaphragm. Count the number of lobes.
Gently lift the liver up and probe it to locate the small,
greenish-brown gall bladder which is on the pig’s right side.
Locate the hepatic duct, which carries bile from the liver to
the gall bladder
Along with the pancreas, the liver and the gallbladder are involved in
the secretion of digestive enzymes. Thus, alhough the food never enters
these organs, they are crucial for the digestive process.
5.
6.
7.
8.
9.
Locate the diaphragm (sheet of thin brown muscular tissue
you cut through ealier), which is the tough muscle that
separates the abdominal cavity from the thoracic cavity.
Find the tube-like esophagus, which lies directly behind the
trachea and joins the mouth and the stomach. Food moves
down the esophagus by muscular contractions after being
softened by saliva in the mouth.
Follow the esophagus from mouth to locate the soft, sac-like
stomach beneath the left side of the liver. The stomach is
filled with acids and digestive enzymes that help break down
food. Motion of stomach muscles also helps macerate food
further (if process not completed by teeth)
With scissors, cut along the outer curve of the stomach (slit
open longitudinally).
Open the stomach and note the texture of its inner walls. The
longitudinal ridges inside the stomach are called rugae and
increase the area for the release of digestive enzymes. The stomach may not be empty because fetal pigs swallow amniotic fluid.
The pig has a digestive system which is classified as monogastric or nonruminant. Humans also have this type of digestive system. They have
one stomach (mono=one, gastric=stomach). Some mammals, especially herbivores, have multiple stomachs (polygastric or ruminant) to help
in the digestion of tough herbaceous nutrition sources.
10. Locate the entrance to the stomach or esophageal area, the cardiac region which is largest, and the pyloric region where the stomach
narrows (constricted caudal portion) to join to the small intestine. The first 3-4 cm of the small intestine is the duodenum.
11. At each entrance of the stomach, there is a sphincter, or ring-shaped muscle to control food entering or leaving the stomach. The
esophageal sphincter separates the esophagus and the stomach, controlling the food that enters the stomach. The pyloric sphincter
separates the stomach and the duodenum, controlling the food that enters leaves the stomach.
Note: Fetal pigs receive their nourishment from their mother through the umbilical cord.
12. Identify the first part of the small intestine, the U-shaped duodenum, which connects to the lower end of the stomach. Pancreatic
juice, made by the pancreas, and bile, made by the liver and stored in the gall bladder are added to food here to continue digestion.
13. Study the rest of the small intestine. Notice that it is a coiled, narrow tube, held together by tissue called mesentery. The soupy, partly
digested food that enters the small intestine from the stomach is called chyme.
14. Check and observe for veins and arteries in the clear mesentery that carry absorbed nutrients to the liver through the hepatic-portal
vein. Note that the circulatory system will then take nutrients from the digestive system to all cells of the body.
15. Carefully cut through the mesentery and uncoil the small intestine. Note and record its length in centimeters. The mid-section is called
the jejunum, while the last section is called the ileum. Each section of the small intestine is dedicated for the absorption of a specific
type of nutrient.
16. With scissors, remove a 3-cm piece of the lower small intestine. Cut it open and rinse it out.
17. Observe the inner surface of the small intestine. Run your finger along it and note its texture. Using a magnifying glass, examine the
villi, the tiny (microscopic) projections that line the small intestine and increase the surface area for absorption.
18. Follow the small intestine until it reaches the wider, looped large intestine. It appears as a compact coil and is larger in diameter than
the small intestine.
19. Cut the mesentery and unwind the usually darker, thicker, and coiled large intestine or colon. Measure and record its length. In the
body, water absorption happens mostly in the large intestine.
20. Locate the junction of the large and small intestine. Below this junction may be found a small pouch-like structure called the caecum.
The caecum has no known function in the pig. This same item is the appendix in humans. It helps in the slow digestion of plant
materials in other mammals. A function that is not necessary in humans (vestigial structure)
21. Notice that the large intestine leads into the rectum, a tube that runs posteriorly along the dorsal body wall. It is the straight end
portion (last 1-2 inches)of the large intestine that stores wastes and carries it to the opening called the anus through where they are
eliminated.
22. Locate the thin, white pancreas beneath the stomach and duodenum. It begins in the loop between the stomach and duodenum and
ends near the spleen on the left side; looks like a clump of about one hundred pinhead-sized grapes. The pancreas makes a variety of
digestive enzymes. Pancreatic juice flows through pancreatic ducts to the duodenum. This duct is difficult to find in a pig.
23. Find the spleen, a long, reddish-brown organ wrapped around the outer curvature of the stomach. It resembles a tongue. The spleen
filters out old red blood cells and produces new ones for the fetus.
24. Label the pig's body organs.
If time remains, continue with Part C: The Respiratory System. Otherwise, clean up your materials and work area. Wrap the pig in
damp paper towels and put it in a zip-lock plastic bag. Clean, wash, and sterilize your lab equipment and return it to the supply cart.
Sanitize table tops and wash your hands thoroughly with soap and water.
Part C: The Respiratory System
The respiratory system is responsible for the exchange of gasses. The pig must take in oxygen to burn food and must rid itself of carbon dioxide
waste once it's born.
Air enters through the external nares. Air is drawn into the nasopharynx or nose chambers where sensory nerve cells detect smell.
1. Be sure to wear your lab apron and eye cover.
2. Examine the diaphragm, a sheet of muscle that stretches across the abdominal cavity and separates it from the thoracic cavity where
the lungs are located. It is anterior to the liver. It is responsible for drawing air into the chest cavity. The fetal pig does not use the
diaphragm because gas exchange occurs through the umbilical cord. The diaphragm in adult pigs moves up and down changing air
pressure in the chest cavity causing air to move into and out of the lungs. Spams of this muscle result in hiccups!
3. In order to see the upper part of the respiratory system, you will need to extend cut #1 up under the pig's throat and make to more
lateral incisions in order to fold back the flaps of shin covering the throat.
4. In the thoracic cavity, carefully separate the pericardium or sac surrounding the heart and the diaphragm from the body wall.
5. Locate the two, spongy lungs that surround the heart (either side) The tissue that covers and protects the lungs is called pleura. The
lungs haven't been used by the fetus so they have never contained air.
Notice that there is a difference in size between the lungs because of the placement of the heart.
6.
7.
8.
9.
Note that there are several blood vessels around the lungs, which come to and or go to the heart. You will study these more closely
during the review of the Part D: Circulatory System. Because of the close link between lungs and heart in reference to
respiration/circulation, some refer to these as the cardiopulmonary system.
Find the trachea, a large air tube that lies anterior to the lungs that extends from the neck to the chest. The trachea is easy to identify
because of the white cartilaginous rings that line it and help keep it from collapsing as the animal inhales and exhales.
Notice that the trachea extends posteriorly from the larynx branches or splits in the chest cavity dorsal to the heart, then going towards
each lung. These two tubes are called bronchial tubes. Inside the lungs these branch into smaller bronchioles that end with a grapelike cluster of air sacs or alveoli where oxygen and carbon dioxide are exchanged with capillaries. Alveoli are the microscopic site of
gas exchange between blood and fluid air (It happens through diffusion across a semi-permeable membrane that allows only carbon
dioxide or oxygen through. As long as a gradient is maintained of more oxygen and less carbon dioxide in the lungs, oxygen will flow
into the blood and carbon dioxide into the lungs. Thus, constant breathing is necessary to intake oxygen and release carbon dioxide).
Dissect along the bronchus of a lung to view branching as it enters it.
Note: Once the heart is removed on the next part, revisit the bronchial tubes as it will be easier to see them at that point.
Note: If there is time, remove a piece of the lungs, and cut it to see its internal structure. Observe under a microscope to see the alveoli.
10. Lying ventral to the trachea or windpipe (anterior surface of trachea at base of the neck), locate the pinkish-brown, V-shaped structure
called the thyroid gland. This gland secretes hormones that control metabolism.
11. At the top, anterior end of the trachea, find the hard, light-colored larynx or voice box. This organ contains the vocal cords that
enable the animal to produce sound and is made mostly of cartilage. Carefully make a mid-central incision in the larynx to see both
sides of the vocal cords better (be careful not to damage any blood vessels).
12. Locate the glottis at the top of the trachea. This flap of skin closes over the trachea whenever you swallow. Find the area called the
pharynx at the back of the nasal cavity. The area of the pharynx that is not part of the mouth (nasal passages/chambers) is called the
nasalpharynx. Sensory nerve cells detect smell in these passages. Air enters an adult pig through the mouth or external nares before
passing through the nasopharynx and down the trachea to the lungs. Starting with the nasal passages, these air ducts are lined with
mucous, hair, and/or cilia to help protect the lungs from debris in the air.
13. Label the diagram of the respiratory system
If time remains, continue with Part D: The Circulatory System. Otherwise, clean up your materials and work area. Wrap the pig in
damp paper towels and put it in a zip-lock plastic bag. Clean, wash, and sterilize your lab equipment and return it to the supply cart.
Sanitize table tops and wash your hands thoroughly with soap and water.
Part D: The Circulatory System
The circulatory system carries nutrients from digestive system to all
body cells, moves chemical messages secreted by the endocrines
system, moves specialized cells and antibodies of the immune
system, moves respiration gases to/from lungs to/from body cells,
and moves wastes from body cells to excretory system.
The circulatory system of the pig, as with other mammals, consists
of the heart, arteries, veins, and capillaries. There are two major
parts to this system. Pulmonary circulation supplies the lungs with
blood. The systemic circulatory system supplies all parts of the
body except the lungs. The blood that goes to the lungs is oxygendepleted and carbon-dioxide rich. The pulmonary circulation
recharges the blood with oxygen, while removing carbon dioxide.
The blood returns to the heart for systematic circulation. The
systemic circulation then pumps the blood throughout the body that
uses the charged oxygen-rich blood, systematically turning it into
carbon-dioxide rich blood, which will then return to the heart to be
pumped into the pulmonary circulation to restart the cycle.
Note: To study the heart, major veins, and major arteries, carefully
remove tissue as necessary to expose the vessels. This is best done
by separating tissue with a blunt probe and by picking away
connective tissue from the blood vessels with a forceps.
1.
2.
3.
4.
Be sure to wear your lab apron and eye cover.
If you have not done so already, you will need to
cut through the sternum (thoracic bone) to open
the thoracic cavity.
Locate the heart. It is covered by a thin, tough,
tissue membrane called the pericardium. Remove
this membrane to study the heart.
Partially covering the heart on its anterior margin
and extending into the neck on each side of the
trachea is the whitish thymus gland. This gland is
part of the immune system and is larger in young
individuals.
Now that the you found both the thyroid and the thymus
gland, carefully cut them away (WITOUT DAMAGING
ANY BLOOD VESSELS), to better expose the heart and the
trachea. View the trachea again now that it will be better
exposed.
5.
6.
7.
Pigs, like all mammals, have four-chambered
hearts. The right side of the heart pumps blood to
the lungs, while the left side of the heart pumps
blood to all other parts of the body. Locate the
right and left sides of the heart.
Each side of the heart has an upper and a lower
chamber. Upper chambers are called atria and
receive blood, while lower chambers are called
ventricles and pump blood out of the heart. Locate
the right and left atrium and ventricle. Touch them with your finger.
Notice that the surface of the heart is covered with blood vessels. These are part of the coronary circulation, a set of arteries and
veins whose only job is to nourish the heart tissue. Blockage in these vessels causes heart attacks.
Note: In general, veins carry blood in and arteries carry blood out of the heart (although the terminology is often used in reference to other
organs. For example, the hepatic vein is the blood vessel that sends blood into the liver coming from the digestive system and the umbilical vein
is the vessel through which blood enters the body from the umbilical cord)
Also note that the pig may have been injected with colored latex which makes it easy to locate the veins (blue) and the arteries (red).
8.
Anterior to the heart, locate another large vein that enters the right atrium. This vein, the anterior vena cava, brings blood to the right
atrium from the anterior part of the body (cranial areas including head, neck, and forelegs).
9. Now lift the heart to view its dorsal surface. Observe the posterior vena cava that carries blood from the posterior (caudal including
all regions posterior to the heart) part of the body and empties it into the right atrium.
Find the pulmonary artery (or trunk), which leaves the right ventricle. It arises from the anterior portion of the right ventricle and
soon divides into the right and left pulmonary arteries that service each lung. After birth, this vessel carries oxygen-depleted and
carbon dioxide rich blood to the lungs for gas exchange. However, in a mammalian fetus, a white shunt underneath the apex of the
heart called the ductus arteriosus allows fetal blood to bypass the lungs and go directly to the aorta, the largest artery of the body.
Until then the ductus venosus, another shunt, is a segment of umbilical vein that goes to the liver and then on to posterior vena cava
carrying blood rich in placental oxygen and nutrients.
10. Locate the pulmonary veins that enter the left atrium coming from each lung. After birth, these vessels carry oxygenated blood from
the lungs to the heart.
Note that the pulmonary circulation is not necessary until after birth when lungs are needed for gas exchange. Also note that during pregnancy
the mother breathes for itself and for its offspring, putting greater strain on lungs. The same is true about the digestive and excretory systems.
They are only active after birth.
11. Identify the aorta, a large artery that transports blood from the left ventricle. Many arteries that carry blood throughout the body
branch off this one. It soon splits into the descending and ascending aortas, that service the caudal and cranial body parts,
respectively. It will then branch further and be named for parts of the body that it leads to. The gastric artery leads to the stomach, the
hepatic artery leads to the liver, the renal artery leads to the kidney, the femoral artery leads to the lower limbs and the carotid artery
leads to the head. Try to locate these arteries. Also. try to locate the jugular vein that brings blood back from the head.
12. Remove the heart by carefully cutting the arteries and veins leading to and from the heart as far away from the heart as possible. DO
NOT damage any lung tissue.
Note: Now that the heart has been removed, the bronchi should be visible. Dissect connective tissue as needed to ease the view. You may also
want to remove the lungs for further study, if time allows
13. Hold the dorsal and ventral surfaces of the heart with your thumb and forefinger and rest the ventricles on your dissecting tray. With a
scalpel, cut the heart through the frontal plane into dorsal and ventral halves. Caution: The scalpel is very sharp. Use it carefully
and always cut away from yourself. ASK FOR TEACHER ASSISTANCE if at any time you are unsure of the procedure.
14. Remove any material inside the heart and expose the walls of the atria and the ventricles.
15. Study the internal features of these chambers and note where vessels leave or enter each chamber. Locate the valves between each
atrium and ventricle. These structures prevent blood from flowing backward in the heart.
16. Identify the right atrium, right ventricle, left atrium, and left ventricle. The valves that prevent the back flow of blood are
the A/V valves and the semilunar valves. A/V valves are found between the atria and the ventricles. The semilunar valves are found
between the ventricles and the pulmonary artery and vein. The structure between the two ventricles is the septum.
17. Label the fetal pig heart diagram
If time remains, continue with Part E: The Urogenital System. Otherwise, clean up your materials and work area. Wrap the pig in
damp paper towels and put it in a zip-lock plastic bag. Clean, wash, and sterilize your lab equipment and return it to the supply cart.
Sanitize table tops and wash your hands thoroughly with soap and water.
Part E: Urogenital System
*MAKE SURE YOU OBSERVE A PIG WHICH IS THE OPPOSITE SEX OF YOURS. YOU WILL BE RESPONSIBLE FOR BOTH THE
MALE AND FEMALE PARTS!!!
The "uro" in urogenital stands for the urinary system. The "genital" portion stands for the reproductive system. Diagram E may help you with
this system. The urinary or excretory system and genital system are structurally related. Therefore, it is convenient to study them together.
Recall that you are dealing with paired structures. What is observed on one side may also be seen on the other.
1.
2.
Be sure to wear your lab apron and eye cover.
Remove the digestive organs to study the excretory and reproductive organs that make up the urogenital system.
Note: You may want to study each of the digestive organs internal structures later (if time allows)
3.
4.
5.
Locate the large, bean-shaped kidneys lying against the dorsal body wall. Look for two lumps low in the abdominal cavity. Notice
that they are covered by the peritoneum. You will need to carefully remove the peritoneum to properly see the bean-shaped kidneys.
Kidneys filter wastes from blood.
Locate the adrenal glands on the anterior surface of each kidney. These glands are part of the endocrine system and secrete hormones
such as adrenaline (controls flight-or-fight response).
Find the renal artery and renal vein (thinner) coming in and out of the kidney. The artery carries blood to the kidney. The vein
carries blood out of the kidney
6.
7.
8.
9.
10.
11.
12.
13.
Find the ureters, tubes that extend from the medial surface of the
concave side of the kidneys near the renal vessels to the bag-like
urinary bladder. It originates from the concave side of the kidney.
They carry the urine produced by the kidneys into the bladder.
Follow the ureter posteriorly until it joins the urinary bladder. Do not
remove any of these organs. The urinary bladder lies between the
umbilical arteries and temporarily stores liquid wastes filtered from
the blood.
Lift the urinary bladder to find the urethra, the tube which carries
urine out of the body Follow the urethra to the urogenital opening on
the outside of the pig's body.
Remove one kidney and dissect it horizontally into 2 halves. See your
text if you need help. Locate the cortex and the medulla on one half of
the kidney. Each of these areas has a specific job in the collection and
processing of body wastes.
Also locate the other parts of the liver including:
1. Cortex
2. Medulla
3. Renal Pyramids
4. Renal Columns
5. Calyces
6. Renal Pelvis
Prepare for the observation of the reproductive organs of the male or female by pulling the hind legs apart.
Make sure that incision #6 extends all the way to the anus but be careful to not cut too deep and damage the internal organs. So if not
done so already, with scissors, cut anteriorly a little to one side of the mid-ventral line to avoid cutting the penis on the male. Press
firmly on the tissue between the legs to feel the cartilaginous structure of the pubic symphysis. This is part of the pelvic girdle.
Continue the incision anteriorly and cut through the pubic symphysis. Expose the urethra.
Follow the directions below for locating the excretory and reproductive organs in either a male or female pig. When you finish
observing the organs in a pig of one sex, exchange specimens with another classmate to view the organs in a pig of the opposite sex.
Male System
8. In the male pig, locate the two scrotal
sacs at the posterior end of the pig.
9. Open one sac and determine the presence
of a testis. The testes descend just before
birth to the outside of the body proper.
This procedure is very important, as the
ordinary temperature of the human body
(98.6°) would kill sperm. The 3-4 degree
lower temperature of the testes outside
the body keeps the sperm viable or alive.
If your specimen is advanced in fetal
development, the testes may have already
descended into the scrotal sacs.
Otherwise, they may be found in a tube
like structure, the inguinal canal, small
oval organs.
10. In either case, locate one of the testes and
note the coiled tubule beginning at
anterior margin of each of the testes.
These make up the epididymis. Follow
this tube forward as it passes through the
inguinal canal as the vas deferens.
Sperm cells produced in the testis pass
through the epididymis for maturating
and into this tube to connection to the
urethra and finally the urogenital duct
that leads to the outside.
11. Follow the vas deferens. This tube
crosses over a ureter and enters the
urethra
12. At this point, as in humans, the urethra
becomes a urogenital duct. This extends to the urogenital open that lies posterior to umbilical cord in reflected flap of body wall
containing urinary bladder. Follow the urethra to the penis, a muscular tube lying just below the skin posterior to the umbilical cord.
In mammals, the penis is the organ that transfers sperm.
13. Make an incision alongside the penis and free it from the body wall. Push it to one side and use scalpel to make a midline incision
through the pelvic muscle and bones. Spread the legs and open the pelvic cavity so that you can dissect out the pelvic organs.
14. Notice a small paired glands on each side of the urethra. These are the that secrete seminal fluid (to help sperm reach destination)
15. Note the very small prostate gland between seminal vesicles on dorsal surface of the urethra. This gland is part of the endocrine
system and secretes male hormones.
16. Another group set of pair glands is on each side of the urethra where it enters the penis. These are the bulbourethral glands, which
secrets fluids to lubricate penis and clear it of urine during sexual act.
17. Label the diagram of the male urogenital system
Female System
12. Spread the legs to separate the pubic
symphysis and thereby expose the
female reproductive system.
13. Locate the oval-shaped ovaries which
are found caudal to the kidneys at the
posterior end of the abdominal cavity.
14. Dorsal to the urinary bladder and
ventral to descending colon, you will
find the oviducts or Fallopian tubes
(uterine tubes), They are twisted and
coiled tubes leading from the ovaries
and are attached to them. On them
secreted eggs will be fertilized in time
for successful uterine implantation.
The egg must develop a little before
being able to attach to the uterine
wall. These tubes carry eggs from
ovaries to the uterus.
15. The oviducts continue posteriorly and
are soon supported by broad
ligaments
16. Further on, the oviducts join to form
the common uterus, where the eggs
implant for embryonic development.
The uterus is dorsal to the urinary
bladder and the urethra.
Note: In pigs, unlike humans, the uterus
forms a Y-shape as opposed to a V shape.
In pigs, the uterus and uterine tubs form a
collective structure called horns
17. Remove or reflect the skin from the
ventral surface of the pelvis. Use scalpel to cut carefully at the ventral midline through the muscles and bones of the pelvic girdle.
Spread the legs and open the pelvic cavity to expose the continuation of the urethra and the remaining organs.
18. You will notice a slight constriction of the common uterus marking the location of the cervix. The cervix can often be a site where
cancer develops in females.
19. Posterior to the cervix, the remainder of the muscular tube that forms the vagina, which is an opening for the male penis enter the
female system. The vagina will appear as a continuation of the uterus. Sperm from the male are deposited into this organ during
mating and must travel into/towards the Fallopian tubes.
20. The vagina and the urethra open into a common area called the urogenital sinus. This cavity opens to the outside at the urogenital
opening. Locate the point where the urethra joins to form the common-urogenital sinus.
21. Label the diagram of the female urogenital system
If time remains, continue with Part F: The Nervous System. Otherwise, when you have completed your study of the urogenital system
of both sexes, then clean up your materials and work area. Wrap the pig in damp paper towels and put it in a zip-lock plastic bag and
return it to storage place. Clean, wash, and sterilize your lab equipment and return it to the supply cart. Sanitize table tops and wash
your hands thoroughly with soap and water.
Part F: The Nervous System
The nervous system controls all body functions and response to the external environment. It includes both sensory, processing systems, and
control systems. The central nervous system consists of the brain, spinal cord, and extending nerves. This dissection is difficult, tedious work
and requires proceeding carefully to avoid destroying important brain tissues.
1.
2.
3.
4.
5.
6.
7.
Be sure to wear your lab apron and eye cover.
With the pig dorsal side down, open both thoracic and abdominal flaps and locate the spinal column.
Select a site along the spine and remove any organs blocking your view of the spine. Using a scalpel, expose the spine and locate any
emerging nerves. Trace one as far as you can into the body.
Place the pig dorsal side up in your dissecting tray. In the thoracic region, remove the skin from the entire skull and muscle to expose
10mm of the vertebral column.
Using forceps to grip the spine and scissors to cut, open the vertebral canal by cutting off the vertebral arch. Note the dura mater
or outermost covering of the brain & spinal cord.
Make a second cut on the other side of this vertebrae, and fold the spine section upward so you can view the cross-section. Locate the
white and gray matter, dorsal and ventral root, central canal, and a dorsal root ganglion.
In order to observe the brain, the skull bone, or cranium needs to be removed. As you cut through the skull near the center, be careful
not to break the meninges or membranes covering and protecting the brain. Insert the point of your scissors just under the bone at the
base of the skull. Angle the tip of the scissors upward so as not to damage the soft brain tissue. Cut forward along the midline of the
brain to the eyes. Cut to either side at the point where you began cutting and the point where you stopped cutting. Gently remove the
cranium by carefully using forceps to break and peel away the piece
The meninges are the membranes which cover the brain. Mammals have three layers of membranes. The dura mater is the outermost, the pia
mater is the inner membrane, and the arachnoid mater lies in between.
8. After the skull is open, chip away the pieces but do not use the scalpel blade for chipping.
9. When the brain is completely exposed , locate the olfactory lobes that control smell are at the front of the cerebrum.
10. Behind the olfactory lobes, locate the 2 large hemispheres called the cerebrum. Fissures indenting the surface of the cerebrum are
called sulci (sulcus, singular). Gyri (gyrus, singular) are ridges projecting outward from the surface. The cerebrum controls sensory
processing, memory, judgment, thinking, etc.
11. Locate the longitudinal fissure or indention that runs laterally between the right and left cerebral hemispheres.
12. Posterior to the cerebrum is the cerebellum. Locate the cerebellum and the transverse fissure that separates it from the cerebrum.
The cerebellum consists of 2 lateral hemispheres and is involved with the control of muscles and coordination.
13. Find the fissure between the right and left cerebellum hemispheres called the vermis.
14. Carefully remove the brain from the skull in order to locate the hind section of the brain known as the medulla oblongata. The
medulla connects the brain to the spinal cord and controls all vital functions of the body such as heart beat and breathing. It also
helps in regulating sensory impulses, hormonal secretions, and general awareness (consciousness).
In humans a series of other structures and glands included the amygdala, the thalamus, the hypothalamus, etc. are also part of the mid and
lower brain and have multiple functions. Refer to Part II of Anatomy Project for more information.
15. Label the diagrams of the brain and spinal cord
Time permitting, feel free to revisit any part of this exercise.
Actually seeing the structures you have been studying in the context of an entire organism plus a free-flowing discussion of their anatomy and
physiology should prove valuable.
Also take time to dissect and/or study any of the organs that have been removed.
Clean up your materials and work area. Wrap the pig in damp paper towels and put it in a zip-lock plastic bag. Clean, wash, and
sterilize your lab equipment and return it to the supply cart. Sanitize table tops and wash your hands thoroughly with soap and water.