Fetal Pig Dissection Manual
Introduction
In this unit you will work in groups of four to go through this dissection manual and dissect your fetal pig. This manual is broken up into sections to aid you in your dissection. Each section provides the necessary instructions and/or background information to complete the section. Review questions based upon the information provided in this manual, previously covered in class, and/or in your textbook are included at the end of each section. Sections should be completed in the order presented. An extra credit section is included for those students who finish the first eight sections with time to spare.
Each student will be responsible for completing the worksheet, which goes along with this manual. This worksheet is composed of two parts, which are explained as follows.
1) A record of activities completed
Most sections have one or more activities, which must be completed. To get credit for a section, each student must get a stamp on their worksheet from their instructor to verify completion of each activity.
2) Review questions
Each section has a number of questions. These questions should be completed prior to beginning the next section of the manual.
For students who finish the required sections of the manual early, several additional sections are included which may be completed for extra credit.
As dissection requires cooperation between group members and the use of sharp-edged equipment, the following rules must be adhered to throughout this unit.
1) All group members must contribute to group activities
Students normally choose to alternate between handling the pig (cutting, etc) and instructing other group members by reading the directions from this manual. Regardless of how your group chooses to allocate responsibilities between members, all members must contribute to this assignment throughout each class period.
2) Each group must return dissecting equipment and the fetal pig at the completion of each class period
Each group will be assigned a set of dissecting equipment. Groups are responsible for returning their equipment to the designated location prior to the end of the class period. It is also the responsibility of each group to place their fetal pig in its bag and return it to the storage area at the completion of each class period.
3) Use care when handling dissection equipment
Take care of your dissection equipment and use caution when handling sharp-edged equipment. Never handle the scalpel blade and don’t play with dissecting needles or probes. Do not use dissecting scissors on anything but your pig.
4) Read all directions before beginning an activity
Never begin a cut without first knowing where you should be cutting (i.e., follow the directions in the manual). Once damaged, tissues will be hard to tell apart and your grade will suffer when it comes time to identify “pig parts” for your instructor. Remember— you can always cut more if needed.
5) Take time to examine your pig closely throughout the activity
The pictures provided in this manual will help you to identify specific structures in your pig. However, individual pigs may vary slightly from the pictures. The most common problem encountered by students is being unable to identify certain structures because they did not follow directions when making their cuts and damaged their pigs.
Section 1 – Origin of Fetal Pig
Domestic pigs (Sus scrofa) are mammals, which are raised for their meat. Pigs are omnivores, meaning that they feed on a variety of both plant and animal matter. The average lifespan of a pig is between 15 and 20 years. Pigs have many anatomical similarities with humans. What this means to you is that you can apply the information you have learned over the past month about human anatomy to your fetal pig.
As their name implies, fetal pigs are unborn animals which are obtained from the uterus of a mature female pig. Fetal pigs are made available for biological study when mature females are butchered for their meat. Your fetal pig has been drained of its body fluids and preserved for dissection.
Review Questions (to be answered on your worksheet)
1) What do pigs eat?
2) What is the typical lifespan of a pig?
3) Why won’t your fetal pig bleed during dissection?
4) How are fetal pigs obtained?
Section 2 – Age of Fetal Pig
The age of your fetal pig can be determined by measuring its length. Body length should be measured along the back of the pig following the curvature of its spine from the tip of the snout to the base (beginning, not the tip) of the tail. Use a string to determine the length of your pig and then determine the length of the string in centimeters with a meter stick. Use the following table to determine the length of your pig and enter your data (both length and age) on the blank in Section 2 of your worksheet (no instructor signature required for this activity).
Length (cm) / Approximate Age (days)1.1 / 21
1.7 / 35
2.8 / 49
4.0 / 56
22.0 / 100
30.0+ / 112-115 (full term)
Review Questions (to be answered on your worksheet)
5) What is the advantage of using a string to measure your pig rather than just using a meter stick?
Section 3 – External Anatomy
Like all other vertebrates, fetal pigs have bilateral symmetry (the right and left sides of their bodies are equal in size and shape). The pig’s body is composed of four regions: a head, a neck, a trunk, and two pairs of appendages (two front legs, two hind legs). The various orientations (top, bottom, sides) of animals such as your pig have been given the following names.
dorsal – near or toward the back (spine) of the pig
ventral – near or toward the underside (belly) of the pig
lateral – near or toward the right or left side of the pig
anterior – near or toward the front (head) of the pig
posterior – near or toward the rear (tail) of the pig
The primary external features of the pig, by region, are presented as follows.
head
mouth – located at the anterior end of the head
eyes –on either side of the head
ears – on either side of the head
snout (nose) –elongated, a pair of nostrils at the anterior end, contains stiff sensory hairs
neck- no prominent external features
trunk
nipples (teats) – located on the ventral surface on both male and female pigs, two rows are present with between five to seven nipples in each row.
body hair – in older fetal pigs body hair is often present
umbilical cord – the umbilical cord, which is lost shortly after birth, is the large structure protruding (sticking out) from the ventral surface of the pig
anus – external opening of the large intestine located near the tail
tail – located on the posterior end of the pig
appendages
forelimbs – also called the front legs
hindlimbs – also called the hind legs
Practice identifying the five orientations (dorsal, ventral, lateral, anterior, posterior) and the primary external features of your pig as presented in this section. When each member of your group is able to identify all five orientations and the primary external features, ask your instructor to quiz your group so that you can receive a stamp for this section on your worksheet.
Review Questions (to be answered on your worksheet)
6) What is bilateral symmetry?
7) What are the four regions of a pig’s body?
8) Define the following words dorsal, ventral, and lateral.
9) What is the function of the umbilical cord?
Section 4 – Internal Anatomy of the Trunk Region
- The body cavity within the trunk region of the pig contains the major organs of the digestive, excretory, circulatory, and respiratory systems. To view the anatomy of the body cavity it is necessary to make several incisions (cuts) with your scalpel and scissors.
- You may use pins to hold down your pig while cutting open the trunk region.
- Begin your dissection by using your scalpel to lightly trace the cutlines shown on Figure 1.
- You will use these lines as a guide to make your incisions.
- Your incisions should be made in the order presented in Figure 1. For the first incision, lift the skin to be cut with your forceps and make a small slit with your scalpel. Insert your scissors into this slit and cut along the cutline you previously traced. Make sure that you do not cut too deep (skin only). When finished with the first incision, make the second incision but make sure not to cut all the way around the right side of the umbilical cord. Continue with incisions 3 through 6.
- After completing your cuts, ask your instructor to view your work so that they can initial your worksheet.
Review Questions (to be answered on your worksheet)
10) What is an incision?
11) What is the purpose of using the string to tie the forelegs and hindlegs during dissection?
12) What is the purpose of making the cutlines prior to beginning the incisions?
Section 5 –The Thoracic and Abdominal Cavities
The body cavity of the pig is divided into the thoracic cavity and the abdominal cavity by a thin muscular wall called the diaphragm. Organs inside these cavities are lined with a thin membrane called a peritoneum.
A number of organs and associated structures can be seen within the thoracic cavity of the pig. A list of the prominent structures is provided as follows.
diaphragm – thin muscular wall which divides the thoracic cavity and the abdominal cavity
lungs – lie within a pleural cavity on either side of the heart, divided into many lobes
heart – located between the lungs and above the diaphragm, divided into four chambers
thymus gland – located at the anterior end of the body cavity immediately above the heart
- Practice identifying these organs and associated structures on your pig using the above text and photos from the dissection manual. When each member of your group is able to identify all of these organs/structures, ask your instructor to quiz your group that they can initial your worksheet.
A number of organs and associated structures can be seen within the abdominal cavity of the pig. A list of the prominent structures is provided as follows.
liver – large brownish organ located below the diaphragm, is divided into two lobes
stomach – a large white organ located on the left side of the abdominal cavity and partially covered by the left lobe of the liver
spleen – located below and slightly to the right of the stomach
small intestine – located below and to the right of the stomach
large intestine – more coiled than the last two regions of the small intestine and located below the spleen
kidney – two bean-shaped structures located next to and partially behind the large intestine, you may have to pull back the intestines and cut through the membrane to view
bladder – a long sac-like structure located below the intestines in the middle portion of the body cavity
- Practice identifying these organs and associated structures using the above text and Photos 1 and 2. When each member of your group is able to identify all of these organs/structures, ask your instructor to quiz your group that they can initial your worksheet.
Review Questions (to be answered on your worksheet)
13) What organs and structures mentioned in this section are contained in the thoracic cavity?
14) What organs and structures mentioned in this section are contained in the abdominal cavity?
Answer the following questions based upon your prior knowledge of anatomy (you may use your book if necessary)
15) What are the four chambers of the heart?
16) What is the difference between arteries and veins?
17) If a section of lung is cut from a fetal pig and dropped into a glass of water it will sink as it contains no air. Give an explanation why the lung of a fetal pig would not contain air.
18) Why is your small intestine coiled?
19) Where does food go after passing through the stomach?
20) List two functions of the liver.
21) What is the function of the kidneys?
Section 6 – The Neck
The neck of the pig contains structures which transport materials between the head and truck of the pig. A list of prominent structures is provided as follows.
larynx – the uppermost part of the trachea, composed of cartilage
trachea – the uppermost part is called the trachea, continues toward the lungs
thyroid gland – a bean-shaped gland below and slightly to the left of the trachea
- Practice identifying these structures using the above text and Photo 3. When each member of your group is able to identify all of these organs/structures, ask your instructor to quiz your group that they can initial your worksheet.
Review Questions (to be answered on your worksheet)
22) What is the larynx made of?
Answer the following questions based upon your prior knowledge of anatomy (you may use your book if necessary)
23) What structures are contained within the larynx?
24) What structure is located at the top of the trachea which keeps food from entering?
25) What is the function of the thyroid gland?
Section 7 – The Mouth
To view the anatomy of the mouth it is necessary to make several incisions with your scalpel and scissors. Begin your dissection by using your scalpel to lightly trace the cutlines shown on Figure 2. The first cutline should be on the right side of the pig and extend from the corner of the mouth to the base of the ears. The second cutline should be the same as the first but located on the left side of the pig. You will use these lines as a guide to make your incisions.
For both incisions, lift the skin to be cut with your forceps and make a slit with your scalpel.
Insert your scissors into this slit and cut along the cutline you previously traced.
After making the two incisions, cut the mandible (lower jaw bone) with your scissors to split the jaws.
A list of prominent structures within the pig’s mouth is provided as follows:
tongue – relatively large muscular structure within the mouth
epiglottis – small flap of tissue at the base of the tongue
glottis – appears as a oval opening of the trachea (windpipe) within the epiglottis, pull the tongue toward the chest to view
hard palate – rigid portion of the roof of the pig’s mouth
soft palate – soft portion of the roof of the pig’s mouth
teeth – located along the maxilla (upper jaw) and mandible within the mouth
- Practice identifying these structures using the above text. When each member of your group is able to identify all of these organs/structures, ask your instructor to quiz your group that they can initial your worksheet.
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Review Questions (to be answered on your worksheet)
26) What is the mandible?
27) What is the glottis?
28) What is the hard palate?
29) What is the soft palate?
30) What is the maxilla?
Answer the following questions based upon your prior knowledge of anatomy (you may use your book if necessary)
31) List one function of a pig’s tongue.
32) Why are some teeth pointed and others relatively flat on top?
Section 8 – The Brain
To view the anatomy of the brain it is necessary to remove the skin and top of the skull from the pig with your scalpel and scissors. Begin your dissection by using your scalpel to lightly trace the cutline shown on Figure 3. The cutline should extend around the top of the head from the top of the pig’s nose to the base of the ears. Make sure your cut extends below the eyes (see Photo 4). You will use this line as a guide to make your incision. For the incision, lift the skin to be cut with your forceps and make a slit with your scalpel. Insert your scissors into this slit and cut along the cutline you previously traced.
After making the incision, cut around the top of the skull (above the eyes) as shown on Photo 4 and remove the top of the skull. Remove the tissues covering the brain carefully to avoid damaging the brain.
A list of prominent structures within the pig’s brain is provided as follows.
longitudinal fissure – a dividing line along the top of the brain which divides the brain into right and left hemispheres (sides)
right cerebral hemisphere – the right half of the cerebrum
left cerebral hemisphere – the left half of the cerebrum
cerebellum – the portion of the brain located behind the cerebrum
- Practice identifying these structures using the above text and Photo 4. When each member of your group is able to identify all of these organs/structures, ask your instructor to quiz your group that they can initial your worksheet.