Pigeon Dissection 595y2a

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 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 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 radiusulna 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 es 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

ed 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. 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 from the pancreas to the small intestine. The Pancreas is a flubby organ that secretes enzymes that 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 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, 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.