Summary:
Pigs are mammals just as humans are. A study of the pig anatomy will allow high school students to better understand the human body. The following is a description of how to dissect a fetal pig.
Objectives:
1. The student will be able to identify the external and internal features of the
pig.
2. The students will learn the unique functions of the organs.
Instructions:
Students may wish to wear gloves and goggles while dissecting. All dissected pig parts should be placed in appropriate containers. After the lab the students should dispose of the fetal pigs, latex gloves, and any other waste according to their teacher's directions. Also dissecting equipment should be washed according to the teacher's directions.

General Observations
1. Identify the four regions of the fetal pig body: the large, compact head ; the neck ; the trunk with four appendages .
Head and Neck Region
1. Examine the head in more detail. Identify the eyes with upper and lower lids, the external ears , the mouth , and the nose or snout . Note the position of the nostrils or external hairs on the snout. Feel the texture of the snout. It is composed of bone, cartilage, and other tough connective tissue and as such, allows the pig to root and push soil and debris in its search for food.
2. Open the pig’s mouth and note the tongue with its covering of papillae , which contain taste buds. Papillae are especially concentrated and prominent along the posterior edges and tip of the tongue. Notice if any baby teeth are present.
Appendages
1. Examine the feet and legs of your pig. The first toe, or digit, corresponds to your big toe or thumb. The second and fifth digits are reduced in size, and the middle two digits, the third and fourth, are flattened or hoofed. Pigs and other hoofed animals walk with their weight of the tips of the digits.
2. Locate and identify the following structures and joints: wrist, elbow, shoulder, ankle, knee, and hip.

Trunk
1. Place the pig on its dorsal surface and examine its abdomen. (Do not tie or pin the pig down yet!) The most prominent feature of the ventral surface of the fetal pig is the umbilical cord seen near the posterior end of the abdomen. During its development, the fetus was connected to the placenta on the uterine wall of its mother’s reproductive system via the umbilical cord.
2. On the ventral surface of the pig the pairs of nipples or teats . Both male and female pigs may have from five to eight pairs of these structures. Finally locate the anus, the posterior opening of the digestive tract. The anus is situated immediately under the tail.
Determine the sex of your fetal pig.
1. The male is identified by (1) the presence of a single urogenital opening to the urinary and reproductive system just behind the umbilical cord. (2) the presence of a swelling on the posterior portion of the abdomen between the upper ends of the hindlimbs. The swelling is the scrotum , which contains the testes , a part of the male reproductive system. Identify the penis , a large, tubular structure immediately under the skin posterior to the urogenital opening.

2. The female is identified by the presence of a single urogenital opening immediately ventral to the anus. A small fleshy piece of tissue, the genital papilla, projects from the urogenital opening.
*Note that in both male and female fetal pigs, there is a common urogenital opening shared by the urinary tract and the reproductive system.
1. With scissors, carefully cut through the corner of the mouth and back toward the ears until the lower jaw can be dropped and the oral cavity is fully exposed.
2. If teeth are not present, cut into the gums and determine whether developing teeth are present.
3. Feel the roof of the oral cavity and determine the position of the hard palate and soft palate. (In your own mouth you can feel your hard and soft palates by touching the superior surface of the interior of your oral cavity with your tongue. The anterior portion is your hard palate. Posterior to the hard palate is the soft palate.) Posterior to the soft palate is the pharynx .
Locate the opening to the larynx , the glottis . It can be identified by the presence of a small white cartilaginous flap, the epiglottis on its ventral surface. The glottis is between the tongue and the esophagus. The epiglottis covers the glottis when a mammal swallows. If you are struggling to find the larynx and pharynx, they can be located later, after you open up the visceral cavity and dissect the throat region.

1. Place the pig, ventral side up, in the dissection pan. Secure the pig by using rubber bands, string or pins. Begin your incision with scissors at the umbilical cord and proceed towards the chin. You should cut through the muscle layer but not too deeply; otherwise the internal organs may be damaged.
2. If your pig is a female , make the second incision completely around (to either side of) the umbilical cord and proceed with a single incision posteriorly for approximately 3 cm between the hindlimbs.

3. If your pig is a male , make the second incision as a half circle anterior to the umbilical cord and then proceed with two incisions posteriorly, and at angles, to the region behind the hindlimbs. The incisions made in the region of the scrotum should be made carefully so as not to damage the testes, lying just under the skin.
4. Deepen incisions until the body cavity is exposed. Proceed carefully, however, as the body cavity may be filled with a dark fluid. In order to make lateral flaps of the muscle tissue (which can be folded out of the way) make incisions as illustrated.

Now, carefully open the body cavity. If it is filled with fluid, pour the fluid into the waste container provided (not into the sink) and carefully rinse out the cavity with a little water.
5. Use your finger to locate the lower margin of the rib cage. Just below it, make an incision laterally in both directions from the first incision. In this region is the diaphragm , a sheet of muscular tissue connected to the body wall and separating the two major body cavities: the thoracic cavity and the abdominal cavity . By using your scalpel, free the diaphragm (do not remove it) where it is in contact with the body wall.

6. Carefully peel back the side flaps and pin them beneath your pig. It may be necessary to cut through the ventral part of the rib cage with a pair of scissors to separate body wall flaps. Do not damage the heart and lungs.
7. To free the umbilical cord and the flesh immediately surrounding it, cut through the umbilical vein and attached tissue. Pin this flap between the hind legs.
8. When the body cavities are fully exposed, carefully remove any excess red or blue latex that may be present.
Endocrine system
Thymus gland , a whitish structure that is divided into two lobes and is in the neck and upper thoracic cavity, it partially covers the anterior portion of the heart and extends along the trachea to the larynx. It plays an important role in the development and maintenance of the immune system.
2. Thyroid gland , immediately beneath the thymus in the neck region, small and reddish, oval shaped and a more solid consistency than the thymus.
Thyroid hormones function in the regulation of metabolism, growth, and development.

Digestive System
1. Liver , consisting of four reddish brown lobes, is located in the visceral cavity posterior to the heart. The liver is a vital organ, serving as the filter and storage organ. It produces bile.
2. Gallbladder : can be found on the undersurface of the pig's right central liver lobe. The gall bladder is a small, greenish sac and is attached by membranous tissue to the underside of a lobe of the liver. Bile is stored here.
It is used for breaking down fats . The bile duct passes from the gallbladder to the small intestine where the bile enters the digestive tract.

3 . Pancreas , carefully move the small intestine, elongated granular mass located between the stomach and the small intestine. This organ supplies digestive enzymes into the intestine and hormones into the blood.
4 . Stomach , a whitish, saclike organ located under the left lobe of the liver. It frequently extends posterior to the liver before opening into the small intestine. Note that the esophagus penetrates the diaphragm before joining the stomach. Feel for the cardiac (cardioesophageal) sphincter and the pyloric sphincter by gently squeezing the entrance and exit of the stomach between your index finger and thumb. (You might need to use the index of your text book to help you find out where the cardioesophageal and pyloric sphincters are.) The stomach serves as the first organ of digestion.
Make a cut in the stomach to expose its contents. The rough surface is called rugae.
5. Small intestine , small tubular extension of the digestive tract serving as the area for final digestion and absorption.
6 . Mesentery , transparent membranes holding the coils of the small intestines together.
7.
Large intestine , the enlargement following the small intestine which extends into the pelvic region. The coiled large intestine terminates into the straight rectum. The large intestine is used for the storage of wastes and the removal of water. To locate the rectum you will need to remove a great deal of muscle tissue, working downward toward the dorsal surface. But, wait to do this until you reach the urogenital part of the dissection.

Respiratory System
1 . Larynx , located anterior to the heart, air passes through the glottis into the larynx. In humans it is the voice box. Make a vertical slit in the larynx to expose the vocal chords.
2 . Trachea , extends from the larynx and divides into two major branches, the bronchi , to the lungs.
Note the cartilaginous rings that prevent the trachea from collapsing. Once exposed, the trachea is easy to identify because it looks and feels just like a vacuum cleaner hose. FORM FOLLOWS
FUNCTION!

3.
Lungs , the reddish purple sacs that are found on either side of the heart dorsal to the liver. Note the right lung consists of four lobes and the left two or three lobes.
Circulatory System
1 . Heart , consists of two atria which have thinner walls and are darker than the ventricles, reddish in color, is enclosed within a pericardial sac. It serves as the pump for the blood. The pericardial sac, which surrounds the heart, may be filled with latex. Remove it with your forceps. Remove the pericardial sac to view the heart.
2 . Coronary artery and coronary vein , are lying in a diagonal groove between the two ventricles. They supply blood directly to the heart.
3 . Superior vena cava and inferior vena cava , gently push the heart to the right and identify these veins.
4.
Aorta , leads dorsally out of the left ventricle of the heart and its base is partially covered by the pulmonary trunk coming from the right ventricle.
5. Spleen , reddish-brown spherical organ located posterior and dorsal to the stomach. This organ is a filter for the removal of red blood cells and the production of antibodies.
Urogenital System
1. Kidneys , situated against the dorsal wall, are covered by peritoneum, the smooth shiny membrane that lines the abdominal cavity. To expose the right kidney and ureter, lift up the abdominal organs and move them anteriorly to the pig’s left. Using a dissecting needle, carefully scrape away the peritoneum so that the kidney, a largish, bean-shaped structure can be seen.

2. Bladder , follow the ureters to the bladder. Then lift the bladder and find the urethra. the urethra is the structure through which urine passes from the bladder to the outside of the animal. In the male, the urethra is very long and passes through the penis to the outside of the body. In the female, the urethra is short and passes posteriorly to join with the vagina.
3. Ovaries , (female) small, yellowish kidney-shaped structures that lie just posterior to the kidneys. They are the site of egg production and female hormones. All of the eggs are present at birth.
4. Uterus and vagina , (female) next to the urethra, also tube-like, the uterus will be anterior to the vagina which is a muscular thick wall. You can find the uterus by tracing the fallopian tubes from the ovaries.
5. Testes , (males) site of sperm production; in older fetuses they are located in the scrotum but in younger fetuses they may be found anywhere between the scrotum and the kidneys. The testes are the primary male sex organs or gonads.
6. Penis , (males) find the bladder, trace this posteriorly to the urethra. This tube-like structure curves anteriorly and enters into the penis. The penis will join the urogenital opening.
7. Vas deferens , tube which extends from the dorsal posterior portion of the testes. Follow the vas deferens to the base of the bladder where it loops over the ureters and enters the urethra. Used for sperm to travel to the penis.
8. Be sure to spend some time identifying the reproductive parts of someone else’s pig who has one of the opposite sex from your own.

Name: Name:
Now that your pig is fully dissected, trace from beginning to end the sequence of structures involved in the following processes:

Digestion

Respiration

Reproduction

Urine production and excretion

Blood circulation
Answer the following questions:
1. What is the function of the umbilical cord?
2. What body system is the spleen a part of and what is its function?
3. What is special about the design of the snout?
4. Briefly describe how you can visually tell the difference between a male and a female fetal pig (not just what parts they have, but how you can recognize them).
5. What symptoms might a newborn baby exhibit that would suggest the possibility that its pyloric sphincter is damaged and will not open? Note:
This is not in your book…think it through.

6. What is the function of the urogenital opening?
7. Compare and contrast the human hand with the pig’s hoof.
8. What difference do you note in the hard and soft palate?
9. What are the two major body cavities of the fetal pig called?
10. What structure separates these two cavities?
11. Why are the thyroid and thymus glands needed?
12. Why is it necessary for the epiglottis to close over the glottis (think about what happens when you accidentally try to breathe and swallow at the same time)?
13. What is the function of the liver?
14. What system contains the cardioesophageal and pyloric sphincters?
Describe their functions.

15. What role do you think the rugae play in digestion?
16. What are the functions of the small intestine and the large intestine?
17. Why is the mesentery needed? In other words, what would happen if the mesentery were not present?
18. What is the difference between the trachea and the esophagus?
19. What function does the pericardial sac serve?
20. What is the role of the kidneys?
21. Gently palpate your own esophagus and trachea. Which is anterior?
22. In step two of the respiratory system section there is a note that says,
“FORM FOLLOWS FUNCTION.” What, specifically, is that statement referring two in terms of vacuum cleaner hoses and tracheae?