Fetal Pig Dissection

The fetal pig that you will dissect has been injected with a colored latex (rubber) compound. The arteries have been filled with red latex and the veins with blue. An incision was made on the side of the neck to enable the injections. The incision can be seen in the photograph below.

Click on the photographs to view enlargements.

External Structures

Obtain a fetal pig and identify the structures listed in the first photograph.

Use the second and third photographs to identify its sex.

Use your pig and also a pig of the opposite sex to identify the structures in the second and third photographs below. The word "urogenital" refers to an opening that serves both the urinary (excretory) and the reproductive systems.

1. Both sexes: Nipples, Umbilical Cord
2. Female: Urogenital Papilla, Anus
3. Male: Urogenital Opening, Penis

Preparation and Initial Cuts

Tie one front leg of the animal with a string that passes underneath the dissecting pan to the other leg. Repeat this with the back leg.

Insert one blade of scissors through the body wall on one side of the umbilical chord and cut posteriorly to the base of the leg as shown in the first photograph below. Continue cutting from the anterior end of this cut so that it resembles an upside-down U. Your finished cut will be anterior to the navel and along each side of the navel. The flap of body wall that contains the navel can be folded posteriorly to reveal the internal organs of the abdomen.

Extend a single cut along the midline of the ventral surface of the animal to about 2 cm. from the chin. Cut completely through the body wall in the abdominal area but keep the cut shallow in the neck region.

The diaphragm separates the abdominal cavity from the heart and lungs. Cut the body wall on each side of the diaphragm as shown below. This will enable you to spread the body wall open without cutting the diaphragm.

Mouth and Neck Region

Use a scalpel to cut the sides of the mouth so that the bottom jaw can be opened for easier viewing (see the first photograph below). You will need to cut through the musculature and the joint that holds the lower jaw to the skull. Open the jaw wide enough so that the glottis and epiglottis are exposed. The epiglottis projects up through the soft palate into a region called the nasopharynx. The hard palate and soft palate separate the nasal and oral cavities. When breathing, air passes through the nasal passages to the pharynx. The pharynx is the space in the posterior portion of the mouth that both food and air pass through. From the pharynx, it passes through the glottis to the trachea.

Below: Hard Palate, Soft Palate, Glottis, Epiglottis, Tongue

Carefully, peel the skin away from the incision in the neck region using a blunt probe (a needle or the point of scissors will do if a blunt probe is not available). Use the probe to peel away muscle tissue until the thymus gland on each side of the trachea is exposed.

Use a probe to separate the two lobes of the thymus gland and to further separate the musculature over the trachea.. The thyroid gland is darker and lies between the posterior ends of the two lobes of the thymus gland.

Below: The thymus gland and their surrounding tissues have been separated to reveal the thyroid gland.

Continue separating the tissue with a probe until the trachea and esophagus are exposed. The esophagus is dorsal to the trachea. The large hard structure attached to the trachea is the larynx. It contains the vocal chords.

Below: Larynx, Trachea, Esophagus

 

Respiratory System

You have already seen the nasopharynx, hard palate, soft palate, epiglottis, glottis, trachea, and larynx. Follow the trachea to where it branches into two bronchi and observe that each bronchus leads to a lung. The left lung contains three lobes and the right lung contains four. Each lung is located in a body cavity called a pleural cavity. Observe how the diaphragm attaches to the body wall and separates the pleural cavities and pericardial cavity (contains the heart) from the abdominal cavity. Contraction of the diaphragm forces air into the lungs.

The lungs can be seen in each of the diagrams below. Notice that the diaphragm separates the abdominal cavity from the pleural and pericardial cavities.

Digestive System

You have already seen how the esophagus leads from the pharynx through the neck region. Using a probe, trace follow the esophagus to the stomach. Identify the small intestine and large intestine (colon). Find the posterior part of the large intestine called the rectum and observe that it leads to the anus. Locate the cecum, a blind pouch where the small intestine joins the large intestine.

Identify the liver. Lift the right lobe and find the gallbladder. This structure stores bile produced by the liver. Find the bile duct that leads to the small intestine. The pancreas is located dorsal and posterior to the stomach. It extends along the length of the stomach from the left side of the body (your right) to the point where the stomach joins the small intestine. Lift the stomach and identify this light-colored organ.

The spleen is an elongate, flattened, brownish organ that extends along the posterior part of the stomach ventral to (above) the pancreas.

Below: 

1. Urinary Bladder, Small Intestine, Large Intestine, Spleen, Liver, Diaphragm, Heart, Lungs
2. Gallbladder, Bile Duct, Stomach, Pancreas
   The liver has been lifted to show the gallbladder attached to the under surface
3. Liver, Spleen, Pancreas
4. Pancreas
   The stomach has been lifted to reveal the pancreas.
5. Small Intestine, Large Intestine, Spleen, Liver
6. Intestine (uncoiled)
7. Intestine (uncoiled)

     

Blood Vessels and Abdominal Organs

1. Heart, Pulmonary Trunk, Pulmonary Artery, Aortic Arch, Ductus Arteriosus, Aorta, Brachiocephalic Artery, Left Subclavian Artery, Coronary arteries
   Blood passes from the left ventricle through the aortic arch and aorta to the body. The first branch of the aorta is the brachiocephalic artery. The second branch is the left subclavian artery which goes to the left leg. After the pig is born, blood leaving the right ventricle passes through the pulmonary trunk and artery and then lungs. Before birth, it passes from the pulmonary trunk through the ductus arteriosus to the aorta. This bypasses the lungs, which are not used before birth.
2. Same as above (different pig)
3. Trachea, Left Common Carotid Artery, Right Subclavian Artery, Left Subclavian Artery, Left Atrium, Right Ventricle, Right Atrium, Aortic Arch, Brachiocephalic Artery, Right Common Carotid Artery, Larynx
4. Right Atrium, Right Ventricle, Posterior Vena Cava
5. Heart, Lung, Liver, Posterior Vena Cava
6. Aorta, External Iliac Artery, Umbilical Artery, Urinary Bladder
7. Renal Artery. The renal artery passes blood from the aorta to the kidney.
8. Renal Vein, ureter, urinary bladder. The renal vein returns blood from the kidney to the posterior vena cava.
9. Right Internal Jugular Vein, Right External Jugular Vein, Right Subclavian Vein, Anterior Vena Cava, Posterior Vena Cava

Heart

The diagram below summarizes the circulatory system of a mammal.

Excretory System

1. Kidney, Ureter, Urinary Bladder. Urine passes from the kidney through the ureter to the urinary bladder.  
2. Uterine Horn, Ovary, Colon
   The small and large intestines have been moved to the side (up in this photograph).
3. Urinary Bladder, Kidney, Umbilical Artery
4. Ureter, Kidney, Colon
5. Renal Vein, Renal Artery, Kidney, Ureter

Reproductive System (Female)

1. Ovaries, Horn of Uterus, Body of Uterus
   The anterior portion of the uterus is divided to form the right and left horn.
2. Ovaries, Horn of Uterus, Body of Uterus, Urinary Bladder
3. Body of Uterus, Urethra, Vagina, Urogenital Sinus, Colon, Urinary Bladder
   The urethra (carries urine from the bladder) merges with the vagina to form a common duct called the urogenital sinus.

Reproductive System (Male)

1. Penis, Testes, Epididymis
2. Bulbourethral Gland, Seminal Vesicles, Urinary Bladder
   The seminal vesicles can be seen at the base (posterior end) of the urinary bladder.