Pigeon Dissection
INTRODUCTION: The bird is a vertebrate whose body plan is adapted to its
requirements for flight. For example, the skeletal system is lightweight and very strong.
The flight muscles of the chest may make up one fifth of the total mass of a bird's body.
Birds have extremely great energy requirements because of their high metabolic rate.
The unique air sacs of their respiratory system provide them with a continuous supply of
oxygen. In line with their needs for a streamlined, lightweight body, birds' reproductive
organs are small and inactive for most of the year. During the breeding season,
however, the male and the female reproductive organs increase greatly in size.
Objective: How does the bird’s body allow it to be maximally strong and light at the
same time?
Vocabulary Terms to Know:
Feather: Rachis, Barbs, After-Feather, Barbules, Hooklets,
Bones- Pneumatic , Sternum (keel) ,Synsacrum, Humerus, Radius, Ulna, Pygostyle,
Furcula, Scapula, Coracoid
Muscles- Pectoralis major, Supracoracoideus, Iliotibialis,
External Features- Nictitating membrane, Cere, Uropygal Gland, Patagium, Ear
Digestive System- Esophagus, Crop, Proventriculus, Gizzard, Liver, Small Intestine,
Pancreas, Cecum, Cloaca
Respiratory- Trachea, Syrinx, Bronchi, “Lungs”, Air Sacs
Urogenital- Testis, Ovary, Magnum (region), Isthmus(region), Uterus(region)
MATERIALS NEEDED: preserved specimen /probe/dissecting tray/forceps/scissors/hand
lens/scalpel PROCEDURE:
EXTERNAL OBSERVATIONS
1.
Pull out one of the primary feathers and examine it with a hand lens. Locate the
long, slender, hollow Main Shaft or Rachis . From the shaft, you will note that barbs
extend outward at an angle of about 45 degrees. With your fingers, gently pull apart the
barbs. Notice that they are formed of still smaller BARBULES with interlocking hooks.
In your notebook draw a feather and label the Rachis, Barbs, After-Feather, Barbules,
and Hooklets. (6pts For drawing and 5 correctly and clearly labeled parts)
2.
Examine the pigeon's head. Look closely at the eye, with its moveable upper and
lower lid. Gently pull the lids back to that you can see the NICTITATING MEMBRANE in
the corner of the eye. This is a characteristic that birds share with reptiles.
At the upper end of the beak is a slit-like nasal opening. Just behind this opening, locate
a white structure called the CERE, which is the fleshy patch at the juncture of the beak
and the head.
Just below and slightly behind the eye, look for the external ear opening. It will be
located under the bird’s feathers.
In your notebook draw the head of a pigeon. Indicate the eye of your bird and show the
Nictitating Membrane. Indicate which way the membrane moves to shut. Also, indicate
where the Cere is located. Finally, indicate where the bird’s ear is located. (4pts =
drawing + Three correctly and clearly labeled anatomical parts.)
3.Before skinning and plucking your bird, hold one wing out to its full extent and feel the
flap of skin between the humerus and the radius-ulna area. This is the PATAGIUM (like
the skin membrane part of a wing, like a bat’s membrane-like wing). There is a tendon
at the anterior (front) border of the patagium. Be very careful not to cut this tendon
while you are removing the skin of the bird.
You should be able to identify this structure .
4. Look for the UROPYGIAL GLAND (“preening gland”) on the bird's back, just above
where the tail feathers insert. This gland, usually a small lobe, produces oil used for
PREENING the feathers.
In your notebook write out why it would be useful for a bird’s feathers to be covered in
oil. (2 pts for using complete sentences)
EXAMINING THE
MUSCLES
5.
Make 4 cuts from the
mid-ventral incision; two into
the wing areas and two into
the leg areas. Fold back the
layers of the skin so that you
can look into the body cavity.
6.
Locate the two large
PECTORALIS MUSCLES, which
are attached to the STERNUM
(or KEEL). A keel in bird
anatomy is an extension of the
sternum (breastbone) which
runs axially along the midline
of the sternum and extends
outward, perpendicular to the plane of the ribs. The keel provides an anchor to which a
bird's wing muscles attach, thereby providing adequate leverage for flight.
In your notebook discuss whether or not you would expect flightless birds to have such a
large sternum. (2pts for complete sentences)
7.
Carefully cut through the one layer of muscle and peel it back to show a second
layer beneath it. The lower layer is called the pectoralis minor muscle. Both PECTORALIS
MUSCLES (major and minor) are the flight muscles. Note their size and mass. Observe these
muscles:
Determine how these birds contract and relax these muscles in order to fly. Once
you have a sufficient answer that you can defend you should call Mr. Smalley
over to demonstrate and explain your idea. (2pts for demo and defense)
8.
Using your scissors carefully cut through
the skin of the left leg. Gently pull back the skin
so that you can see the muscles of the leg. NOTE:
You may have to cut through the connective
tissue to free the muscle tissue from the skin. As
you look at the muscles of the leg, locate the
ILIOTIBIALIS MUSCLE, which is the broad, heavy
muscle of the upper leg.
Discuss why these leg muscles are so useful for
jumping. (2 sentences)
9.
the pigeon’s feet- its texture and the
presence or absence of feathers. Look for the
perching tendons located under the skin of the
leg! ( + 3pts for dissecting this out and showing it
to Mr. Smalley and getting his signature signature .)
10. Using a scalpel, cut through all the connective tissue holding the pectoral muscles
in the keel.
11. Using a pair of scissors, cut through the keel just to the left of the midventral line.
NOTE: It does not matter if you crack the keel bone. Your purpose in cutting it is to
reveal the internal organs. Remove any connective or fatty tissue that is still clinging to
the organs of the digestive system. Be careful in the neck reagion not to damage the
crop, which lies just beneath the skin at the base of the neck.
Weigh your bird including the entire pectoral muscle. Remove your pectoral muscle and
then weigh it a second time. What percent of the total bird’s weight is simply it’s
pectoral muscle. (5pts for weighing and showing the math for this exercise)
DIGESTIVE SYSTEM
For an animal to use food as fuel, it must digest the food - break it down small enough
to be absorbed into the bloodstream - and get rid of the waste products. A bird's gut
looks much like your own, but there are some differences. Many seed and grain-eating
birds have a crop connected to the esophagus. The expandable crop allows birds to
quickly gather and store a large amount of food, then retreat to safety to digest it.
12. Locate the thin-walled flabby tube or ESOPHAGUS, in the neck of the bird. This
tube is the first part of the digestive system that is visible to you. Of course, the food
enters the mouth and then passes down
into the esophagus. The lower part of the
esophagus widens into a large, hard
object called the CROP. The crop is where
food is stored until parents can feed their
young. Crop milk (a mixture of lipids and
proteins) is also secreted here for baby
food!
13. A bird has two stomachs (we have
one) to digest its food in record time. In
four hours, a Spur- winged Goose can
digest the same meal that it takes a
rabbit 24 hours to digest. In the upper
stomach, the PROVENTRICULUS (right
after the crop). In this part of the
stomach, digestive enzymes secreted by
glands break down food that has passed
into the stomach.
14. The lower stomach, the ventriculus,
or GIZZARD, is a tough, muscular organ
which crushes and grinds up the food, just like our teeth do for us. Remember a bird has
no teeth, so it swallows food whole. Birds that eat plants and seeds have more powerful
gizzards than meat and fish eaters. The gizzard may contain small stones or pebbles to
help “grind” the food.
Locate the INTESTINE which follows after the GIZZARD. Look for the large, lobed LIVER,
which overhangs the intestine. If you separate the coils of the intestine, you should be
able to see the PANCREAS. Look for the pancreatic ducts which pass from the pancreas
to the small intestine. The Pancreas is a flubby organ that secretes enzymes that pass
into the junction of the small and large intestine- the Duodenum
15. Examine the lower end of the intestine. You should be able to find two saclike
CAECA. The caeca are at the juncture of the intestine and the rectum. It holds bacteria
that helps to further digest plant material.
16. Locate the CLOACA which is the common exit of the digestive tract, reproductive
organs, and urinary organs. You may be able to find the ducts leading from the kidneys
to the cloaca.
In your notebook you will make a schematic diagram of how food “flows” through the
body of a pigeon. Start at the esophagus, include the crop, proventriculus, gizzard, liver,
small intestine, pancrease, duodenum, large intestine, cecum and cloaca.
(11 points)
(you will receive an additional 5 points for including a brief notes of what each of the
organs in the digestive system does)
RESPIRATORY SYSTEM, AIR SACS, & HEART
See your “Respiratory System of a Bird” packet for more information. Lungs exchange
oxygen and carbon dioxide between the blood and air. Bird lungs are smaller than those
of mammals, yet they are part of the most efficient respiratory machinery known in
vertebrates. Even with this efficient respiratory system, birds breathe rapidly during
flight - up to 450 breaths per minute for a pigeon.
17. Unique to birds are AIR SACS. Air sacs act as a bellows to suck air into the body,
and then circulate it in a one-way flow through the lungs - giving the lungs a constant
flow of fresh air.
18. The nine air sacs also act as a cooling system since birds do not have sweat
glands. They contribute to stability in flight by lowering the center of gravity and act as
shock-absorbers in diving birds, such as Brown Pelicans. During courtship, male grouse
inflate special air sacs on their chests like brightly colored balloons to attract a mate.
The lungs of birds feature out-pocketings filled with air which extend between various
organs and penetrate certain bones; they have few blood vessels and no respiratory
surfaces. The sacs are transparent and noticeably thin-walled, resembling soap bubbles.
19. To be seen, the respiratory system needs to be artificially inflated. Cut the trachea
(windpipe) in the neck region; insert a pipet and blow through it (see instructions
below). The lungs and air sacs should become distended and more prominent. There are
9 air sacs.
20. Make a mid-ventral incision through the body wall for the entire length of the
abdominal cavity. Pull the internal organs carefully to one side and blow into the
trachea as described above.
21. If the dissection has been done correctly to this point the abdominal AIR SAC
should be visible. It will resemble an asymmetrical soap bubble. See how many other
sacs you can find and identify (they can be very difficult to see). If you have cut the
respiratory system at any point previously, the air sacs will not inflate and will not be
visible.
(Demonstrate this air sac inflation and explain its significance to Mr. Smalley for credit.
3pts)
HEART
A bird's HEART is much like yours - A FOUR CHAMBERED MUSCLE that pumps blood
throughout the body. A bird's heart weighs up to twice as much as that of a mammal of
equal size because flying is strenuous. Energy-hungry muscles need a bigger, faster
beating heart to send them plenty of oxygen and nutrients. Smaller birds and mammals
lead fast-paced lifestyles and generally have faster heart rates than large ones.
Hummingbird 600 beats per minute at rest, Pigeon 200 beats per minute at rest, Ostrich
65 beats per minute at rest, Human 70 beats per minute at rest.
In the throat region, locate the TRACHEA (windpipe) which is ventral to the
esophagus, except where the crop bulges over it. Run your fingers over the surface of
the trachea. You should be able to feel the tracheal rings which provide form to the
wall. Trace the trachea down to its lower end, where there is a somewhat swollen
chamber. This chamber, which includes specialized internal membranes, is called the
SYRINX. The syrinx, an organ found only in birds, is the organ from which birds produce
their various calls and songs (“Syrinx = Sing”).
22. Trace the syrinx down to its base, where it divides into two smaller tubes called
BRONCHI. Each bronchus leads to a LUNG. The lungs are relatively small organs. Look
for two flattened structures pressed against the ribs and lying on either side of the
vertebral column. Unique to the birds is a system of air sacs that extend out from the
lungs.
23. Look for the pigeon’s HEART in the center of its chest cavity. It will probably be
about 3cm long. Look for the major vessels entering and leaving the heart. Trace the
blood vessels that join the heart and the lungs.
24. Using your scalpel, carefully make a lengthwise cut through the heart, starting at
the lower lip and moving toward the anterior end. The cut should separate the heart
into a ventral part and a dorsal part. You should now be able to see the chambers of the
bird's heart
(you will be filling out a sheet that compares the hearts of different organisms for credit
on this section)
UROGENITAL
SYSTEM
25. In your study of the digestive
system, you probably came across
the KIDNEYS. You will look at the
kidneys and other parts of the
urinary system a little more closely
now. Locate the dark, three-lobed
kidneys. They are just below the
lungs and fit into a depression in
the dorsal wall of the bird.
26. Look for narrow ducts, or
URETERS, leading from the kidney
to the CLOACA. Note that the bird
has no urinary bladder. During
most of the year, the genital
system of the bird is much
reduced in size. You will probably
have a male or female bird with its
reproductive organs in this
inactive stage. If you have a male
bird, look for two white TESTES,
the male reproductive organs. The testes are ventral to the kidneys and may be slightly
anterior to them. Locate the two narrow SPERM DUCTS that lead from the testes to the
cloaca. If you have a female pigeon, look for the OVARY on the left side of the body. The
ovary is in about the same position as the left testis would be. The right ovary in birds is
nonfunctional.
27. Locate the flaring end of the OVIDUCT, which should open close to the ovary.
Trace the oviduct down to its posterior end, which will empty into the cloaca. The size of
the ovary and oviduct will vary, depending on whether the bird died during the breeding
season or
during the reproductively inactive period.
28. Each kidney is made up of three lobes. The ureters emerge from the rear border of
the anterior lobe, pass over the ventral surface of the two posterior lobes, and then
back to the “urodaeum” (uro-genital chamber). On the anterior ventral surface of each
kidney is a small yellowish ADRENAL GLAND.
29. The TESTES in the male are two white ovoid bodies (variable in size with breeding
condition) lying on the ventral surface of the anterior lobe of the kidney. Convoluted
and narrow VASA DEFERENTIA lying lateral to the ureters connect the testes to the
urodaeum then cloaca.
30. In most female birds there is only the left ovary and oviduct lying on the ventral
side of the left kidney. The ovary is irregular in shape due to the different sizes of ova.
SKELETAL SYSTEM
31. Turn your attention to the pectoral region of the skeleton. It is a tripod of paired
bones, the SCAPULA, CORACOID, and FURCULA (or “Wish-Bone”). The scapula is a thin,
bladelike bone tied to the ribs by ligaments, the stout coracoid bone unites the scapula
and sternum. Both muscles that ddepress the wing (pectoralis) and those that raise the
wing (supracoacoideus) are attached to the sternum.
32. Where scapula and coracoid unite, there is a hallow depression, into which the ball
of the chief bone of the wing, the HUMERUS, fits. The supracoracoidus is attached by a
tendon to the upper side of the humerus so that it bulls from below by an ingenious
“rope-and-pulley” arrangement. In this way, the muscle weight is kept below the center
of gravity, providing greater flight stability.
32. The last rib-bearing thoracic vertebra is fused with twelve vertebrae to form a thin
plate-like structure called the SYNSACRUM . This very light but stout arrangement
provides further rigidity to the body frame. Finally, at the end of the bird note the four
caudal vertebra fused to form a PYGOSTYLE. This is analogous to our tailbone, and like
our tailbone it is a vestigial structure from the bird’s Therapod ancestors.
33. The bones of the forelimbs are highly modified for flight. Note how the wing folds
into a compact A shape when the bird is at rest. Identify the humerus and locate the
expanded dorsal surface for the attachment of the pectoral muscles. The RADIUS and
ULNA are longer than the humerus, and the ulna, the larger of the two, carries the
secondary flight feathers. Most modified are the wrist digits which carry the primary
flight feathers.
Unlike many other organisms the bird’s bones are “PNEUMATIZED”. That means that
they are penetrated by extensions of the air sac system and thus contain buoyant warm
air rather than bone marrow. Some diving birds have thick bones to help them
submerge.