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 birds 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, AfterFeather, 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 birds 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 birds 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 radiusulna area. This is the PATAGIUM (like the skin membrane part of a
wing, like a bats 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 birds 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 pigeons 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 birds weight is simply its 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 pigeons 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 birds 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 birds 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.