FETAL PIG DISSECTION
Background information and procedures
Read the background information below; then answer lab report questions 1 and 2.
Background information
Mammals are warm-blooded vertebrates (animals with internal backbones made of
individual bones called vertebrae) that have hair or fur, bear live young, and nourish their young
with milk produced in mammary glands. The placental mammals are the largest group of
mammals. Placental mammals develop completely inside their mother’s uterus before they are
born. During this time of development, these mammals are connected by the umbilical cord to
the placenta, a capillary-rich organ that attaches to the wall of the uterus. There, nutrients and
oxygen from the mother’s blood are exchanged with wastes and carbon dioxide from the blood
of the developing young, or fetus. In this investigation, you will be studying the fetal pig. An
in-depth examination of this organism will help you to better understand the features and body
systems of all placental mammals, including humans.
External features of the pig
1.
2.
3.
Put on gloves if you will be handling the pig.
Obtain a fetal pig and lay it on its side in a dissecting tray. Point out (touch with a blunt
probe or a finger tip as you name the structure) the major body areas of the pig to your
partner(s):
 head
 neck
 trunk (including chest and abdomen)
 tail
Use figure 1 (on the last page) to help you point out the four ends/ surfaces of the pig.
(These terms will be used in various places in this lab, so you must be familiar with
them.)
 anterior end
 posterior end
 dorsal surface
 ventral surface
Answer lab report question 3.
4.
5.
6.
7.
Examine the pig’s head. Point out the eyelids, the external ears, and the nostrils.
Study the pig’s appendages (legs). Point out the toes, “ankle,” “knee,” “wrist,” and
“elbow.”
Study the ventral surface of the pig. Point out the tiny bumps (nipples). These are
present in both sexes. In the female, these structures connect to the mammary glands.
Locate the umbilical cord. With scissors, cut across the cord to leave about 1 – 2 cm of
it attached to the body. Examine the three openings visible on the cut surface of the
umbilical cord. The largest (which may have blue plastic in it) is the umbilical vein,
which carries blood from the placenta to the fetus. The two smaller ones (which may
have red plastic in them) are the umbilical arteries, which carry blood from the fetus to
the placenta. Point out these three blood vessels.
Answer lab report questions 4 - 8.
8.
Use Figure 2 as you examine the ventral and posterior surfaces of the pig. Point out the
anus, which is in the same position in both sexes. Then locate the urogenital opening,
following the instructions below. (The urogenital opening is the opening which allows
urine and reproductive cells to leave the body). This will allow you to determine the sex
of your pig.
 In a female, the urogenital opening is located just ventral to the anus; a small fleshy
flap called the papilla surrounds this opening.
 In a male, the urogenital opening is located just posterior to the umbilical cord.
(Another external clue that a fetal pig is a male is a slightly swollen region on the
trunk posterior to the hind legs – this is the undeveloped scrotum.)
 Point out the urogenital opening in your pig. Then find a lab group whose pig is a
different sex than yours, and point out the urogenital opening in that pig. Also, point
out the papilla in the female and the scrotum in the male.
Answer lab report question 9.
Abdominal cavity – focusing on digestive organs
9.
Place the fetal pig ventral side up in the dissecting tray. Tie a string securely around one
of its “wrists,” run the string under the tray, pull the string tight, and tie it to the other
“wrist.” Repeat this procedure with another string, tying it to the pig’s “ankles.” This
will help hold the pig in place as you work on it and examine it.
10.
Study Figure 3. The lines show the first set of incisions you will make.
 Begin by pulling upward on the umbilical cord and inserting the point of your scissors
through the skin and muscle layer just to one side of the umbilical cord. Cut next to
the row of nipples on each side of the umbilical cord. You will know if you have cut
deeply enough if you can see a fairly deep opening or some liquid (which may be
brownish or bluish). Once you have cut deeply enough to be through the abdominal
wall, keep the tips of your scissors pointed upward to avoid cutting too deeply.
 After you have cut around both sides of the umbilical cord as Figure 3 indicates, cut
towards the sides of the body near the hind legs and below the rib cage to form two
flaps. Open these flaps, and cut the umbilical vein which seems to be holding the
umbilical cord to the liver.

11.
You should now be able to see the organs of the abdominal cavity. If there is brown
or blue material in the abdominal cavity, rinse it out with running water (hold the
entire dissecting pan in the sink).
Point out the following abdominal structures:
 diaphragm – a sheet of muscle that separates the abdominal cavity from the chest
cavity.
 liver – a large brown structure (the most obvious structure in the abdominal cavity)
 stomach – a soft sac found beneath the liver on the pig’s left side
 small intestine – find the point where it connects to the stomach. Then note that this
coiled, narrow tube is held tightly together by a filmy layer called the mesentery.
The mesentery’s blood vessels absorb digested food from the small intestine, and the
mesentery itself keeps the small intestine coils from tangling with each other.
(continued)
 large intestine – the first part of this tube is very tightly coiled and bound together;
further along, it straightens out as it travels along the midline of the abdominal cavity
just inside the back. This straight section of the large intestine is called the rectum.
 appendix – a blind pouch located where the small intestine joins the large intestine
 spleen – a long, flat, reddish organ wrapped partly around the stomach on the pig’s
left side. The spleen is one of the main locations where white blood cells hide out to
wait for pathogens to show up and filters out old red blood cells.
 pancreas – a thin, somewhat reddish structure located underneath the stomach. It is
covered by a filmy membrane which you will need to remove to see the pancreas
clearly. The texture of the pancreas is different from other organs you’ve seen; it
seems to be made of many tiny spheres stuck together.
 gall bladder – a small sac attached underneath the liver. Note the tiny tubes which
carry bile to the gall bladder and then to the small intestine.
Answer lab report questions 10 – 12.
Abdominal cavity – focusing on excretory and reproductive organs
12.
Move the digestive organs gently to one side of the body cavity if necessary so that you
can study the organs of the excretory (urinary) and reproductive systems. Do not remove
any organs completely from the body. Study figures 4 and 5 as you continue with the
following steps.
13.
Point out the following structures:
 kidneys – the large, bean-shaped structures lying against the dorsal body wall. Note
that they are covered by a membrane.
 bladder – the long tubelike structure which lies inside the abdominal wall. The two
red umbilical arteries are attached to either side of the bladder. The end of the
bladder nearest the umbilical cord has no opening; the opening of the bladder is at its
most posterior end.
 ureters – tubes extending from the kidneys to the bladder. You will need to carefully
remove the membrane covering the ureters to see them clearly.
14.
If you have a female pig, point out the following structures:
 ovaries – small bean-shaped structures
 Fallopian tubes – coiled; attached to the ovaries
 uterus – the structure where the two Fallopian tubes meet. Some of the uterus is
“hidden” behind the bladder and urethra.
15.
If you have a male pig, point out the following structures:
 vas deferens – thin tubes emptying into the urethra at the base (posterior end) of the
bladder. In most male pigs, the other end of each vas deferens will pass through the
abdominal wall.
 testes (if they are still in the abdominal cavity) – these always develop in the
abdominal cavity at first. At some point, usually but not always before birth, the
testes move down into the scrotal sacs through openings in the abdominal wall. Most
of the male fetal pigs we use will already have had the testes descend into the
scrotum, but some males will still have testes in the abdominal cavity.
16.
If your pig is a female, continue with steps 17 and 18, and skip steps 19 - 21. If it is a
male, skip steps 17 and 18 and continue with steps 19 – 21. In either case, you will be
examining how the excretory, reproductive, and digestive systems connect to their
external openings (the urogenital opening and the anus).
17.
If your pig is a female, make an incision along the midline of the body from the
abdominal cavity to the anus. (Do not cut into the anus or the urogenital opening.) You
will need to cut deeply through muscle and the semi-solid pelvic bones. A scalpel often
is helpful in making this incision.
18.
At the posterior end of the female pig, point out two tubes:
 the rectum, which connects to the anus and lies closest to the dorsal surface of the
pig
 the urogenital sinus, which connects to the urogenital opening. Follow this toward
the abdominal cavity. Point out where it divides into two tubes:


the tube which lies closest to the ventral surface of the pig is the urethra; it
connects to the bladder.
the tube between the urethra and the rectum is the vagina; it connects to the
uterus.
19.
If your pig is a male, observe the skin of the abdomen posterior to the umbilical cord.
Point out a muscular tube lying just below the skin. This tube is the penis. In the male
pig, as in many mammals, the penis is normally retracted inside the skin; it only extends
outside (through the urogenital opening) when the male is trying to mate.
20.
Make an incision along the midline of the male’s body from the abdominal cavity to the
anus. (Do not cut into the anus or the urogenital opening, and do not cut through the
penis.) Point out the two scrotal sacs, one on each side of the body in the scrotum. Slit
the membrane covering one of the sacs and point out the testis and the coiled epididymis
inside the sac.
21.
At the posterior end of the male pig, point out two tubes:
 the rectum, which connects to the anus and lies closest to the dorsal surface of the
pig
 the penis, which makes a “U-turn” inside the body and connects to the bladder. The
part of the tube which runs from the bladder toward the posterior end of the pig is
usually called the urethra; the part of the tube which runs from the posterior end of
the pig to the urogenital opening near the umbilical cord is called the penis.
22.
Find a lab group whose pig is a different sex than yours, and point out all the structures in
steps 13 – 21 that are present in their pig.
Answer lab report questions 17 - 19.
Chest cavity – focusing on circulatory and respiratory organs
23.
Make an incision along the ventral midline of the pig, beginning just above the
diaphragm and extending to the “wart” on the pig’s chin. Then, just above the
diaphragm, cut towards each side of the body; make similar cuts toward the pig’s
“armpits;” this will form upper flaps on each side of the body. Open these flaps to
observe the organs in the chest cavity. (You may need to cut through some membranes
to see some of the organs.)
24.
Point out the following structures:
 lungs
 heart
 pericardial sac (the membrane which surrounds the heart)
 diaphragm
 rib cage
 left and right atria (the small, dark brown chambers of the heart)
 left and right ventricles (the large, muscular, light brown chambers). You can’t see
the internal wall separating these two chambers, but you can tell where it’s located by
observing the blood vessels forming a diagonal line on the outside of the heart. These
blood vessels are the coronary vessels (artery and vein).
 coronary vessels (These blood vessels supply food and oxygen to the heart muscle
cells; if they get blocked, the heart muscle cells will die, causing a heart attack.)
 pulmonary artery. This is one of the large blood vessels at the top of the heart.
 aorta. This is another large blood vessel at the top of the heart; in addition, you can
find it behind the left lung towards the midline of the body (don’t remove the lung
completely; just move it to one side). The esophagus is also visible, running parallel
to the aorta; the esophagus is flatter, because its walls collapse flat when nothing is
traveling through it.
 vena cava. You will need to move the right lung to one side; you should be able to
find the posterior vena cava (coming from the lower part of the body) as well as the
anterior vena cava.
25.
Deepen the incision from the pig’s chest up towards its chin, along the ventral midline of
the body. Point out the following structures:
 larynx - a large, hard structure at the anterior end of the “windpipe”
 trachea – an air tube formed from rings of cartilage (it looks a little like a vacuum
cleaner hose). The cartilage rings hold the trachea open at all times; without them,
the trachea would collapse shut whenever you inhale.
 esophagus – in this part of the body, the esophagus lies just dorsal to the trachea and
runs parallel to it; the two are connected by some membrane which you can remove.
 thyroid gland – a pink, oval structure attached to the ventral side of the trachea.
 there’s lots of other gland tissue in this part of the body; it’s part of the thymus
gland, which is much larger in babies that it is in older individuals. The thymus
gland is part of the immune system; this is where T cells develop.