Background Information

PROCEDURE

Part I: External Anatomy

Place your pig in a dissecting tray. Using a ruler, measure the length of the pig from the snout to the tail. Use Figure 1 to estimate the age of the fetal pig.

a) Estimate and record the age of your fetal pig.

Identify the four regions of the pig’s body: the head, the neck, the trunk, and the tail.
Place the pig on its dorsal surface and observe the umbilical cord. Locate the paired rows of nipples along the ventral surface of the pig. Both males and females have these nipples.

b) What is the function of the umbilical cord?

Use the diagrams to determine the sex of your pig. In females, the urogenital opening is located immediately below the anus. A small, spiked tissue called the genital papilla projects from the urogenital opening (see Figure 3). In males, the scrotum containing the testes can be located just below the anus. The urogenital opening of the male is found immediately posterior to the umbilical cord (see Figure 4).

c) What is the sex of your pig?

Examine the feet of the fetal pig.

d) Indicate the number of toes.

Part II: The Abdominal Cavity

During the dissection you will be directed to examine specific organs as they become visible. Remove only those organs indicated by the dissection procedure. Proceed cautiously to prevent damaging underlying structures.

With the pig still on its dorsal surface, attach one piece of string to the pig’s ankle and another to its opposite wrist. Pull each piece under the dissecting pan and tie together. Repeat the procedure for the other wrist and pull once again so that the ventral surface is exposed.
Using scissors, pinch the skin and make an incision just in front of the umbilical cord. Cut toward the anterior of the pig. Follow the incision shown in Figure 5, which is indicated as #1.
Follow the incision markers, indicated in the diagram as #2, toward the posterior of the pig. Make an incision near the neck, indicated by #3, and then at the posterior portion of the abdominal cavity, indicated by #4. Make a lateral incision near the posterior portion of the ribs, indicated by #5. This incision runs parallel to the diaphragm, which separates the thoracic cavity at the anterior of the animal from the abdominal cavity, near the posterior of the animal.
Pull apart the flaps along incision #5, exposing the abdominal cavity. Use the scalpel to tear the connective tissue, the peritoneum, which holds the internal organs to the lining of the body cavity. Now pull apart the flaps of the skin covering incision #4 to expose the posterior portion of the abdominal cavity. Use pins to hold back the flaps of skin.
Locate the liver near the anterior of the abdominal cavity. Using a probe, lift the lobes and locate the gall bladder. Follow the thin duct from the gall bladder to the coiled small intestine. Bile salts, produced in the liver, are stored in the gall bladder. The bile duct conducts the fat emulsifying bile salt to the small intestine.

e) How many lobes does the liver have?

f) Describe the location of the gall bladder.

Locate the stomach beneath the liver. Using forceps and a probe, lift the stomach and locate the esophagus near the anterior junction. Locate the small intestine at the posterior junction of the stomach. The small intestine is held in place by the mesentery, a thin, somewhat transparent connective tissue. Note the blood vessels that transport digested nutrients from the intestine to the liver.
Using the scalpel and forceps, lift the junction between the stomach and small intestine, removing supporting tissue. Uncoil the junction and locate the gland called the pancreas. Recall that the pancreas produces a number of digestive enzymes, hormones, and sodium bicarbonate.

g) Describe the appearance of the pancreas.

Locate the spleen, the elongated organ found around the outer curvature of the stomach. The spleen stores red and white blood cells. The spleen also removes damaged red blood cells from the circulatory system.
Using a scalpel, remove the stomach from the pig by making transverse cuts near the junction of the stomach and the esophagus, and near the junction of the stomach and small intestine. Make a cut along the mid-line of the stomach, open the cavity, and observe. Finally, rinse the stomach and view the lining under a dissecting microscope.

h) Describe the contents of the stomach.

i) Describe the appearance of the inner lining of the stomach.

Part III: The Thoracic Cavity

Carefully fold back the flaps of the skin that cover the thoracic cavity. You may use dissecting pins to attach the ribs to the dissecting tray.

j) What organs are found in the thoracic cavity?

k) How is the abdominal cavity separated from the thoracic cavity?

Locate the heart. Using forceps and a dissecting probe, remove the pericardium from the outer surface of the heart. The large blood vessel that carries blood from the liver to the right side of the heart is called the inferior vena cava (recall that the right side refers to the pigs right side). Blood from the heart enters the right side of the heart thought the superior vena cava. Both the superior and inferior vena cavae are considered to be veins because they bring blood to the heart.

l) Describe how the blood flows through the heart, beginning at the vena cavae.

Make a lateral incision across the heart and expose the heart chamber.

m) Compare the size of the wall of a ventricle with that of an atrium. Why does the left ventricle contain more muscle than the right ventricle?

Locate the spongy lungs on either side of the heart and the trachea leading into the lungs.

n) Why do the lungs feel spongy?

Place your index finger on the trachea and push downward.

o) Describe what happens.

p) What function do the cartilaginous rings of the trachea serve?

Part IV: The Urogenital System

Using scissors, remove the intestines and what remains of the stomach.
Refer to the diagram of the thoracic cavity and urogenital system and locate the kidney. Using forceps and a scalpel, carefully remove the fat deposits that surround the kidney.

q) Describe the shape and color of the kidneys.

Locate the thin tube leading from the kidneys. The ureter carries urine from the kidney to the bladder. Cut into the kidney and note the large number of tubules.

If your pig is a male, refer to steps 23 and 24. If your pig is a female, refer to steps 26 and 27. Make sure that you also view the organs of a pig of the opposite sex from your specimen.

Use the diagram of the male urogenital system to locate the testes. If your fetal pig is advanced in development, the testes may have descended into the scrotum; however, they will probably be found in the inguinal canal. Like the ovaries, the testes develop inside the body cavity. The lower temperatures of the scrotum promote the proper development of sperm cells.
Use the diagram to locate the vas deferens, which conducts sperm cells from the testes to the urethra.

r) Indicate why the male reproductive system is often referred to as the urogenital system while the female’s is not.

Use the diagram of the female reproductive system to locate the ovaries. The ovaries can be found immediately posterior to the kidneys.
Locate the fallopian tubes leading from the ovaries. The fallopian tubes are supported by the broad ligaments. Follow the fallopian tubes, which meet to form the uterus. The fallopian tube is the site of fertilization. Once fertilized, the egg travels to the uterus, the site of the embryo and fetal development. Locate the vagina and follow the canal into the uterus. The constriction that marks the division between the vagina and uterus is known as the cervix.