Name ____________________________
Date _________________
Mammalian Dissection – Fetal Pig
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 by-product of the pork food industry so they aren't
raised for dissection purposes, and they are relatively inexpensive.
External Anatomy
1. Lay the pig on its side in the dissecting pan and locate dorsal, ventral, & lateral surfaces. Also
locate the anterior and posterior ends.
2. Begin with the anterior end of the pig. Identify the head, noting 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, which helps the pig hear by focusing the sound. Note the presence of hair on your pig.
3. Progress along the trunk of the pig; note the neck, forelegs, and hind legs. Examine the
number and arrangement of toe like appendages on each foot.
4. On the ventral surface examine the umbilical cord. It is the connection between the mother’s
placenta and the fetus. The placenta of the mother functions to filter the fetal blood, and
provide nutrients and oxygen to the developing fetus. There are three vessels involved in this
process. The largest is the umbilical vein, which carries blood from the placenta to the fetus.
The two smaller vessels are the umbilical arteries which carry blood from the fetus to the
placenta. Locate the umbilical cord, and cut across the cord about 1 cm from the body.
5. Determine the sex of your pig. The reproductive structures of a pig are internal, and both
males and females have rows of nipples. In order to determine the sex of your pig, you must
locate the urogenital opening. This is the 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. You will also notice a slight enlargement of the scrotal sacs. In
the female, the opening is below the tail, near the anus, in a spike-like genital papilla. Make
sure you observe a pig of each sex.
6. With scissors, make an incision in each corner of the pig's mouth. Your incision should extend
posterior through the jaw. Spread the jaws open and examine the tongue.
7. Observe the palate on the roof of the mouth. The anterior part of the palate is the hard
palate, while the posterior part is the soft palate. Locate the epiglottis, a cone-shaped
structure at the back of the mouth. Above the epiglottis, find the round opening of the
nasopharynx. This cavity carries air from the nostrils to the trachea. Dorsal to the glottis, find the
opening to the esophagus. Examine the tongue and note tiny projections called sensory
papillae. (taste buds) Note the teeth of the pig.
Internal Anatomy of the Fetal Pig
8. Use two pieces of strong twine and tie one around a wrist and
one around an ankle of the pig. Pull each under the dissecting
pan and tightly tie the twine to the opposite wrist or ankle.
9. Make incisions as indicated in the diagram. Cut carefully with
scissors to avoid damaging the underlying organs. Note--when
you cut through the thoracic cavity, you will encounter bone.
You must cut through this bone to expose the underlying organs.
10. Cut the skin flaps back close to the back bone so they will remain
open. Be careful not to injure the kidneys. Pull back the two
flaps of skin (you will need to cut the diaphragm along the sides)
and muscle to view the internal organs. Locate the umbilical vein
inside the abdomen. Once determined, cut it and lay back the
cord and its strip of skin.
THORACIC CAVITY
11. Observe the pericardium, a thin, tough membrane surrounding the heart. Locate the 2 atria
and 2 ventricles. Note the difference in texture and colour.
12. The pig may have been injected with colored latex which makes it easy to locate the veins
(blue) and the arteries (red). Try to trace and identify as many of the blood vessels off the
heart as possible. You may be able to locate the anterior and posterior vena cava, the
pulmonary veins which carry blood from the lungs to the left atrium. The most noticeable
artery is the aorta. The aorta curves to the left and passes cranially along the dorsal side of the
thoracic and abdominal wall. The next largest artery is the pulmonary artery. It arises from the
anterior portion of the right ventricle and soon divides into the right and left pulmonary
arteries.
13. Find the trachea, a tube that extends from the neck to the chest. It is white and lined with
cartilage. The enlargement at the anterior end of the trachea is the larynx (voice box) which
contains the vocal cords. Lying atop the trachea, locate the pinkish-brown, V shaped structure
called the thyroid gland. This gland secretes hormones that control growth and metabolism.
The trachea splits in the chest cavity into two bronchi, which lead into the lungs.
ABDOMINAL CAVITY
Digestive System
14. The large, reddish-brown organ that occupies much of the abdominal space is the liver.
Gently lift it up and locate the gall bladder which is on the pig’s right side.
15. The diaphragm (a thin brown muscular tissue) is the tough muscle which separates the
thoracic and abdominal cavities. The esophagus goes through it to the stomach. The
esophagus carries the food from the pharynx to the stomach. Locate the stomach on the
upper left side of the abdominal cavity, underneath the liver. The stomach resembles a
pouch in appearance and is connected to the esophagus at its anterior end.
16. Observe that the small intestine is not loose in the abdominal cavity but is held in place the by
the mesentery, a thin clear membrane. Check and look for veins and arteries in the
mesentery that carry absorbed nutrients to the liver through the hepatic-portal vein. The large
intestine appears as a compact coil and is larger in diameter than the small intestine. Locate
the junction of the large and small intestine. Below this junction may be found a small pouchlike structure called the caecum. This is the same item that is the appendix in humans. It helps
in the slow digestion of plant materials in other animals.
17. Follow the large intestine (colon) to the rectum. This lies in the dorsal wall of the abdominal
cavity and is the straight end portion of the large intestine. Water is absorbed by the body in
the large intestine. Waste material stored in the rectum leaves the body through the anus.
18. Locate the pancreas which is a large white granular organ located below the stomach. The
pancreas makes a variety of digestive enzymes that travel to the small intestine through the
pancreatic duct. This duct is difficult to find in the pig. The red elongated organ extending
around the outer curvature of the stomach is the spleen. It resembles a tongue. The spleen
helps destroy old red blood cells.
Urinary and Reproductive Systems
19. To find the kidneys, look for two lumps low in the abdominal cavity. They are behind a
membrane called the peritoneum. You will need to carefully remove the peritoneum to see
the bean-shaped kidneys.
20. Locate the ureter originating from the concave side of the kidney. Follow the ureter posteriorly
until it joins the urinary bladder. The urinary bladder lies between the umbilical arteries and
temporarily stores liquid wastes filtered from the blood.
21. Male: Find the scrotal sacs at the posterior end of the pig (between the legs), testis are
located in each sac. Open the scrotal sac to locate the testis. On each teste, find the coiled
epididymis. Sperm cells produces in the teste pass through the epididymis and into a tube
called the vas deferens (in humans, a vasectomy involves cutting this tube).The penis is difficult
to find, but can be located by cutting away the skin on the flap near the umbilical cord. This
tube-like structure eventually exits out the urogenital opening, also known as the urethra.
22. Female: In the female pig, locate two bean shaped ovaries located just posterior to the
kidneys and connected to the curly oviducts. Trace the oviducts toward the posterior to find
that they merge at the uterus. Trace the uterus to the vagina. The vagina will actually will
appear as a continuation of the uterus and will be difficult to distinguish.