Download Ornithology BIOL 456 LAB HANDOUT 2 Avian Anatomy and

Ornithology
BIOL 456
LAB HANDOUT 2
Avian Anatomy and Integument
Slides
Avian Skin: Examine the slide of a cross-section of avian skin with the microscope provided.
Use the figures on pp. 86-87 in your manual to locate structures on the slide that are shown in the
diagram.
Avian skin, unlike mammals, lacks sweat glands, but birds do have other localized glands. The
uropygial gland, for instance, is located at the base of the tail and produces a waxy oil used by
the bird to preen and waterproof its feathers. This gland is not found in all birds (e.g., most
ratites), but is large and prominent in aquatic species.
Avian Lung: Examine the slide of a cross-section of the avian lung. Notice the hundreds of tiny
openings, or air capillaries, and the larger openings, or bronchi. The bronchi branch from the
trachea and carry air to smaller and smaller branches until reaching the capillaries where the
oxygen is absorbed by the blood. The avian lungs, with their complement of 8-9 air sacs, form
part of a complex system of breathing that is more efficient than mammals and helps in flight.
The lungs alone are smaller per body volume than in mammals.
Avian Blood: Examine the slide of avian blood cells. You see hundreds of red corpuscles or
erythrocytes. Birds can have up 5.9 million corpuscles per cubic mm of blood. The corpuscles
also are nucleated, similar to reptiles, but unlike mammals. The dark spot in each corpuscle is
the nucleus. The average life span of a corpuscle is about 2-3 weeks, after which it is replaced
by new blood formed in the bone marrow in adult birds, but also formed in the spleen and liver
in passerines.
Soft Anatomy
This portion of the lab is intended for you to become familiar with internal organs and soft
anatomy of birds. You will work in pairs and each pair will receive an injected pigeon for
dissection. These pigeons are preserved in a mixture of water, methyl alcohol and formalin and
it is recommended that you wear latex gloves while handling the specimen. Gloves will be
provided in lab as well as dissecting tools. Use the diagrams in your manual as a guide to
complete the following sections. You need to learn only the structures given in bold print below.
First, refamiliarize yourself with the external anatomy that you learned in Lab 1. Orient the
bird so that you can recognize dorsal and ventral surfaces. These terms are commonly used in
anatomical descriptions. Also note the location of the uropygial (preen) gland and cloaca (p.
100-101). In the pigeon, it is a small stub located just above the dorsal base of the tail feathers.
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To begin your dissection, place the bird on its back in the dissecting tray exposing its ventral
surface with the feet towards you. You will begin by removing the skin (and all feathers) by first
peeling back the skin down the midline of the bird and along the keel of the sternum. Make a
shallow incision on the belly to start removing the skin, but be careful to not cut too deeply into
the body cavity. Note the feather tracts and subcutaneous (skin) muscles while you are doing
this. When you get to the wings, carefully peel the skin away from the dorsal and ventral
surfaces so that no muscle layers are damaged. Peel the skin away down to the end of the
carpometacarpus. As you do this, you will have to cut the base of the primaries and secondaries
to remove them, but leave the bases of these feathers clearly visible. Next, read the figure
caption on p. 105 and see if you can count all the primaries (there are 10) and secondaries (14,
but they are numbered to 15) in proper order on the wing. In addition, note the difference in
eutaxic versus diastataxic wings and see if you can find the gap between the 4th and 6th
secondaries on your specimen. After skinning the bird, you probably will see an area of fat
deposits at the base of the neck above the sternum. This sternal fat can be seen through the skin
in live birds and is used to estimate condition of birds captured in mist nets. Also note the crop,
or extension of the esophagus, next to the sternal fat deposits. The crop is not found in all birds,
but it is used to store and soften food before is passes on to the stomach (proventriculus). In
many of the specimens, the crop may still contain seeds.
After removing all of the skin and feathers, you will have all the body muscles of the bird
exposed. Use the diagrams in Chapter 6 of your manual to identify the muscles described below-you only need to know those muscles given in bold print on this handout, not all the ones shown
in the diagrams. Learn the origin, insertion, and action for each of these muscles (see pp. 160161 and p. 170 in your manual).
On the ventral surface, note the hard edge of the keel of the sternum running down the
midline. On either side is the large pectoralis major muscle, which originates from the keel and
body of the sternum and furculum and inserts on the deltoid crest of the humerus. It acts to
depress or pull the wing down in flight. Use a scalpel or scissors to cut down through this
muscle next to the keel on one side, then along the proximal and distal margins, so you can peel
this muscle off to the side. Below this muscle and against the keel you will find another muscle,
the supracoracoideus (see p. 157). This muscle also originates on the keel of the sternum, but it
inserts on the dorsal surface of the humerus after passing through a small opening, the triosseal
canal, at the junction of the scapula, coracoid and furculum (see p. 157). The supracoracoideus
muscle elevates or raises the wing in flight. Try to trace the muscle and locate the triosseal
canal. This design allows the bird to keep its two major flight muscles, each with opposing
functions, in the same central area of the body. Why would this be important?
Other muscles to locate in the wing include the triceps brachii, biceps brachii, tensor
patagialis longus, and the groups of muscles that are extensors and flexors. In the leg, locate
the iliotibialis, the gastrocnemius, the tibialis anterior, the group of flexors, and the flexor and
extensor digitorum longus.
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Digestive System (Chapter 7). Identify the structures given here in bold print and learn the
functions of each. Open the mouth of the pigeon and locate the tongue, glottis (opening to
trachea) and esophagus. Use a probe to trace each opening in the mouth into their respective
tubes. Follow the trachea and esophagus into the neck and distinguish these structures there as
well. Open an incision along the ventral midline of the bird from the cloaca to the neck to
expose the inner organs. You will probably cut open the thin-walled crop, an extension of the
espophagus, while doing so. Note the small ridges on the inside of the crop to help break down
food. You will have to use scissors to cut through the sternum along the base of the keel. Pull
the sternum off to the side and expose the body cavity. Locate and identify the liver (right and
left lobes), proventriculus (stomach), gizzard, duodenum, pancreas, small intestine, large
intestine, colic caeca (or ceca), and the cloaca. After identifying these structures, cut open the
proventriculus and gizzard and note the differences in thickness of muscles forming these organs.
The relative size and function of these stomachs varies among birds based on their diet. Do
NOT remove the heart or other structures while completing this dissection!!
Urogenital System (Chapter 10). Identify the structures given here in bold print and learn the
functions of each. Find the three lobes of the kidney on either side of the dorsal wall of the body
cavity. The kidneys are drained by the ureter, a small tube that extends into the urodaeum of
the cloaca. Note here and in figure on p. 223 that the cloaca is subdivided into three chambers.
Make a longitudinal incision along the cloacal wall to open this structure and see if you can find
the three chambers, the coprodeum, urodeum, and proctodeum. Next locate either the testes
or ovaries depending on the sex of your bird. The testes will appear as small oblong lobes near
the kidneys and have a small tube, the vas defrens, leading from them to the urodaeum. This
tube often is found in association with the ureter and carries sperm from the testes to the cloaca.
The ovaries will appear as a mass of small eggs, or ova, of various sizes and development. A
tube leading from the ovary to the urodaeum is the oviduct, through which the developing egg
passes. Depending on the maturity of your specimen, the testes or ovaries may be very small or
quite large. In most birds, only the left ovaries increase in size and become functional as adults.
Why would this be? Note: you are responsible for knowing both male and female structures so
you will need to look at other pigeons in the lab besides your own.
Circulatory System (Chapter 8). Identify the structures given here in bold print and
understand the general pattern of blood flow through the bird. Locate the heart and identify the
left and right atria and ventricles. Do NOT remove the heart as you will need it for reference
to trace veins and arteries. The pigeon has been injected so that arteries (carry oxygenated
blood away from the heart) are red and veins (carry deoxygenated blood to the heart) are blue.
One exception is the pulmonary arteries to the lungs, which are blue, and carry deoxygenated
blood away from the heart.
Locate the jugular veins in the neck and trace them down to where they enter the right and
left precava veins above the heart. These last two veins, with the inferior vena cava, return
deoxygenated blood from the body back to heart where it enters the right atrium. This blood
then passes into the right ventricle and is pumped to the lungs via the pulmonary arteries,
where it is reoxygenated. Now trace the posterior vena cava distally from the right atrium to
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where is passes along the dorsal body wall and note where it branches into the common iliac
veins, which drain the abdomen, kidneys, legs, and tail (p. 195).
The oxygenated blood from the lungs returns to the left atrium of the heart via the
pulmonary veins, passes into the left ventricle, and then is pumped to the body via the aortic
arch and brachiocephalic arteries (see p. 199). Note that the aortic arch is branching to the
right. This is opposite of mammals in which the arch branches to the left. Find the two large
brachiocephalic arteries extending from the aortic arch at the top of the heart. The first vessel to
branch off of these, on each side, is the common carotid artery which carries blood to the brain.
The aortic arch also continues distally along the dorsal wall of the body as the large abdominal
aorta (p. 191, the large central artery without a label), which further branches to the intestines
and kidneys. Become familiar with the general pattern of blood circulation in the bird.
Sense Organs: cut away the skin around the eye (see p. 251) and locate the scleral ring, formed
by a series of scleric ossicles. The ring helps support the eyeball and is the origin for two small
muscles, the Crampton’s and Brucke’s muscles, that aid in focusing the eye. Open the eye and
find the lens inside and note its shape.
Locate the external ear opening behind the eye (see p. 258). Find the auricular feathers and
peal back the skin to expose the ear opening. Look for the tympanum, or eardrum, and see if
you can find the columella, or stapes, inside the ear.