Dissecting the Fetal Pig

Introduction to Mammals Of all the classes of animal life, mammals are considered to be the most advanced. Examples: dogs, cats, squirrels, pigs, whales, horses, sheep, and HUMANS! Vary greatly in size…from 2 inches (the shrew) to 100 feet long (the blue whale)

Mammalian Characteristics Vertebrates (have backbones) Presence of lungs (breathe air) Warm-blooded (endothermic) This means that the body temperature of a mammal stays the same, no matter what the outside temperature is 4 chambered heart

Mammalian Characteristics, cont’d Give birth to live young Monotremes – mammals that lay eggs EX: the platypus and the echidna (spiny anteater) Body Hair Produce milk (have mammary glands) Platypus Echidna

Mammalian Characteristics, con’t Less Obvious Characteristics The diaphragm separates the heart and lungs from the stomach Lower jaw has one bone on each side Different types of teeth adapted to different uses (tearing, chewing) Brains are much more highly developed than any other animal

Comparative Anatomy Study of similarities and differences in the anatomy (structure) of organisms Many aspects of structure and function are identical between different species of mammals Homologous Structures – same structure (embryologically speaking), different function (have a common evolutionary descent) EX: wings of bats and arms of humans Analogous Structures – different structure, same function (evolved in a similar environment) EX: wings of bats and wings of insects

Comparative Anatomy Fetal Pigs Humans Kingdom Animalia Phylum Chordata Class Mammalia Order Artiodactyla Primates Family Suidae Hominidae Genus Sus Homo Species Scrofa sapiens

Why Fetal Pigs? The fetal pig is a mammal, like humans. Nearly all the structures are the same or very similar in anatomy. Fetal pigs are NOT bred for the purpose of dissection. They are a by-product of the pork food industry. Fetal pigs are NOT killed for the purpose of dissection. Those that are not dissected are used for fertilizer or discarded. Fetal pigs are relatively inexpensive. Even in the extra large size, when the structures are well-developed, they can be obtained for about 1/3 the cost of a similarly sized cat. Most people do not think of pigs as “pets.”

Advantages to Dissection Dissection is a hands-on, investigatory kind of activity for students. Dissection allows students to "test the truthfulness" of what they see in books. Dissection impresses on students the normal variation that is present in the natural world. No two fetal pigs, even though they are perfectly normal, will look exactly the same. In fact, to do well on practicals, students MUST looks at several examples of each structure in different animals. Occasionally, quite significant anatomical variations (anomalies) will be noticed.

Safety and Handling Sharps All Dissecting tools should be considered dangerous. Notify your teacher IMMEDIATELY if you are cut. Handle probes, dissection scissors, razor blades, etc. with extreme caution. Always cut away from you, never toward yourself or another person. Dissection specimens should be properly mounted in the dissection pan before cutting.

Safety and Handling, cont’d Do not place your hands near your mouth or eyes while handling preserved specimens.  Most of the preservatives in use today are non-toxic to the skin, but they may cause minor skin irritations.  If the preservative gets on your skin, wash with soap and warm water. If the preservative gets in your eyes, rinse them thoroughly with the safety eyewash. Wear lab gloves and goggles at all times! Lab gloves and paper towels go in the regular trash.  Skin and pieces of pig go into the separate plastic bag at the front of the room (NOT down the sink).

Dissection Helpful Points Actual cutting should be kept to a MINIMUM Tissue are picked and teased apart with needle probes, forceps, and blunt probes in order to trace the pathways of blood vessels, nerves, muscles, and other structures. NEVER CUT OR MOVE MORE THAN IS NECESSARY TO EXPOSE A GIVEN PART. Compare dissections with other students, especially students whose pig is of a different sex. You will be responsible for both sexes on the lab practical (test).

Determine the Sex of your Pig Female:  Look for a single urogenital opening just ventral to the anus.  A prominent genital papilla projects from the urogenital opening.  Male:  Look for the scrotum, a sac-like swelling containing the testes and located ventral to the anus.  The male urogenital opening is faintly visible just posterior to the umbilicus.  Note that males as well as females have multiple nipples = teats = mammary papillae.

Female Male