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.

Objectives:    

Materials:
preserved fetal pig, dissecting pan, dissecting kit, dissecting pins, string, plastic bag, metric ruler,  paper towels

Pre-lab:
Before observing internal or external structures of the fetal pig, use your dissection manual, textbook, and dissection notebook to answer the pre-lab questions on the fetal pig. You may have to refer to more than one dissection manual to answer all the questions so trade and share with other dissection groups.

Click here for Prelab worksheet

***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.

Day 1 - External Anatomy   

  1. Obtain a fetal pig and rinse off the excess preservative by holding it under running water. Lay the pig on its side in the dissecting pan and locate dorsal, ventral,& lateral surfaces. Also locate the anterior and posterior ends.

  2. A fetal pig has not been born yet, but its approximate age since conception can be estimated by measuring its length. Measure your pig's length from the tip of its snout to the base of its tail and record this on your hand-in. Use the length/age chart on this sheet or the inside cover of your dissection manual to determine the age of your fetal pig & record this.

  3. Examine the pig's head. Locate the eyelids and the external ears or pinnae. Find the external nostrils.

  4. 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.

  5. Locate the umbilical cord. With scissors, cut across the cord about 1 cm from the body. Examine the 3 openings in the umbilical cord. The largest is the umbilical vein, which carries blood from the placenta to the fetus. The two smaller openings are the umbilical arteries which carry blood from the fetus to the placenta.

  6. Lift the pig's tail to find the anus. Study the ventral surface of the pig and note the tiny bumps called mammary papillary. These are present in both sexes. In the female these structures connect to the mammary glands.   

  7. 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. In the female, the opening is ventral to the anus. Record the sex of your pig.
  8. 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.
  9. With scissors, make a 3-cm incision in each corner of the pig's mouth. Your incision should extend posteriorly through the jaw.
  10. Spread the jaws open and examine the tongue.
  11. 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.
  12. 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, a large tube in the thoracic which supplies air to the lungs.
  13. Dorsal to the glottis, find the opening to the esophagus. Examine the tongue and note tiny projections called sensory papillae.
  14. Examine the teeth of the pig. Canine teeth are longer for tearing food, while incisor are shorter and used for biting. Pigs are omnivores, eating plants and animals.
  15. Label the drawing of the inside of the pig's mouth.
  16. Clean up your materials and work area. Wrap the pig in damp paper towels and put it in a zip-lock plastic bag. Obtain a piece of masking tape and label your bag with your names. Return your lab equipment and pig to the supply cart and then thoroughly wash your hands with soap.

Click here for Day 1 Worksheet

Day 2      Part A: The Incision 

  1. Be sure to wear your lab apron and eye cover. Obtain your dissecting equipment and pig from the supply cart.
  2. Place the fetal pig ventral side up in the dissecting tray.
  3. 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.
  4. Study the diagram below. The dashed lines numbered 1-5 show the first set of incisions that you will make. 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.
  5. With scissors, make the incisions in order, beginning with 1. Be sure to keep the tips of your scissors pointed upward because a deep cut will destroy the organs below. Also, remember to cut away from yourself.
  6. 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.
  7. Spread the flaps of the body wall apart. Cut the umbilical vein which extends through the liver.
  8. 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.

If time remains continue with part B, the digestive tract. Otherwise, clean up and return your materials and pig as you did on day 1.

Click here for day 2 worksheet

Part B: Digestive System 

  1. Be sure you are wearing your lab apron and eye cover.
  2. Locate the diaphragm, a sheet of muscle that separates the abdominal cavity from the thoracic cavity. Find the most obvious structure in the abdominal cavity, the brownish-colored liver. Count the number of lobes.