First, vertebrates (animals with backbones, including birds and people) have "bilateral symmetry," literally this means "two sides look alike." This means that you can cut a vertebrate in half from only one angle and get two (mostly) equal parts. Circles don't have bilateral symmetry, you can cut a circle in half many different ways and get two full half circles.
Generally bilateral symmetry is easy to see on the outside of an animal (we have two eyes, one on each side of the head, and so forth), but sometimes this is difficult to see with internal organs, but it's generally true nonetheless.
In order to talk about direction on a body, we can't use terms like "north" or "south," which are perfectly good on a map, but don't make any sense with a cat. So biologists use some terms specific to vertebrates, here there are five:
1. Dorsal: the back, in most animals, the topmost side. In vertebrates this is the side closest to the spine. Also can be used as a direction, e.g. the backbone is dorsal to the heart.
2. Ventral: the area opposite the dorsal, the belly region. In vertebrates, the side farthest from the spine. Also can be used as a direction, e.g. the heart is ventral to the backbone.
3. Lateral: to either side, left or right. Also can be used as a direction, e.g. the hand is lateral to the heart.
4. Anterior: forward, toward the mouth end. Also can be used as a direction, e.g. the mouth is anterior to the heart.
5. Posterior: rearward, toward the tail. Also can be used as a direction, e.g. the tail is posterior to the heart.
Now that you've got some idea of the general directions, here are some specific parts of the body that are useful to know. Some may seem obvious, but they are useful to remember when referring to the location of other parts.
1. Head: anteriormost part of a bird, contains the bill (or beak), the eyes and the ears.
2. Crown: the topmost part of the head. This is the area where you might find a crest on a cardinal or cockatoo.
3. Gular region: The area directly ventral to the bill. In pelicans this area is quite large and bare of feathers and forms a pouch. If a bird gets too hot, it may flutter the skin in the gular region to help cool itself, much like a dog pants.
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