Animal bones
When you were younger did you play at being animals? Probably everyone has sometimes wondered what it would be like to be another form of life. Many people have wondered what it would be like to be a bird and a few have even glued feathers to themselves and jumped off the end of a pier. Sadly they always landed in the sea. In some science fiction films people are shown changing into other creatures. Let us imagine what would happen if you changed into a bird and flew away.

If an animal is to fly it needs to be light in weight, have strong muscles to flap its wings, have a strong framework of bones for the flight muscles to hold on to and have a large wing surface to beat the air. If we look at your body we find a heavy body, muscles which can raise and lower your arms, a flexible spine and no wing surface to beat the air. How might your body change?

First the skeleton may change to make a rigid framework for the flight muscles. The spine would become shorter and as it contracted up your back your hip bones would grow longer to fill the space left behind. At the same time the smaller number of bones in the spine would lock firmly together and in the middle of the back to make a rigid support and the hip bone would stick firmly to its end so the whole of the back remained steady during flight.

While a rigid back was forming, the end of each rib would be changing too. An extra growth of bone would begin to stick out like a finger and point to the rib behind. In a short time the finger of bone would reach the rib and stick to it. When this happened, the rib cage became a firm framework under the backbone to support the flight muscles.

When we pretend to fly, we wave our arms up and down but when a bird flaps its wings, it moves them in another way. If we are to move our arms like a bird moving its wings we must do the following. Put your arms out at your sides with the palms of your hands facing forwards. Now bring your hands together as if to clap your hands with your arms outstretched. Next swing your arms back as far as they will go. If you keep swinging your arms backwards and forwards you will get an idea of what it is like to flap your wings. However your body will have to change in a few more ways yet before you can take off.

Hold out your right arm with palm facing forwards. Put the fingers of your left hand in the flesh on the front of your shoulder and move your arm forwards and backwards. You should be able to feel some muscles at work near your shoulder. These muscles are quite weak because you do not spend much time moving your arm in this way. A bird needs much larger muscles because it spends a great deal of time flapping its wings. If your body was to change into a bird's body the next thing that would happen would be the growth of your breastbone. It would have to stick out perhaps half a metre in front of your chin. The muscles in your chest would also swell up to join it so it would seem as if you were carrying a barrel in front of you. Clearly, birds do not look like this so the body must then tilt forwards. Your neck would lengthen and become more flexible so that it could now hold your head, with its beak, facing forwards.

There would be changes in your limbs too. Your arms would become longer and you would lose your third and fourth fingers. The bones would have air spaces in them for extra lightness. At the same time your legs would lengthen. This would raise up your body so that when you beat your wings the ends would not crash into the ground.

Finally your skin would sprout feathers. The feathers on the wings would be very long and form a broad surface to push against the air. If you jumped and flapped your arms with a body like this you could fly away over the rooftops.

How does a bird breathe?
Like us it has a pair of lungs but it also has much more. There are structures called air sacs that grow out of each lung. They are like balloons and make air spaces all over the body even in the bones, including the skull. When the bird breathes in, the air flows through the lungs and into the air sacs. When the bird breathes out, the air passes from the air sacs, into the lungs and out through the nostrils on the beak.

Why does a bird have these extra air spaces?
They make the bones lighter in weight so it is easier to fly. They also allow the lungs to take more oxygen from the air because the air passes twice through the lungs at every breath. The flight muscles of the bird need large amounts of energy to work and taking in the extra oxygen helps the bird release this energy from food.

Does a bat have the same kind of skeleton as a bird?
A bat skeleton has a few features in common with a bird skeleton. The breastbone sticks out a little, but not as far as the bird breastbone. Some of the backbones are stuck together to make a firm support during flight. However there are quite a few differences. In a bat's wing all five fingers are present and the legs are not long and supportive to let the bat stand up on the ground. The lungs do not have air sacs and the bones have marrow in them. Despite these differences, bats manage to fly successfully but they have not been able to live in as many different places as birds.

Do all animals have bones?
No. There is a large group of animals that have bones. They are called the vertebrates. This group is divided into five smaller groups. They are the fish, amphibians, reptiles, birds and mammals. A very large group of animals do not have bones. They are called the invertebrates.

Do all animals with bones have a skull and a spine?
Yes, they do. The shape of the skull may vary greatly to suit the animal's way of life. A crocodile, for example, has a skull with a long snout. This holds a huge number of teeth to help the animal catch its prey. Birds skulls have bones which make the shape of the beak and mammals' skulls can be long and thin, as in the anteater, or have a short snout as in many bats.

Are horns made of bone?
The horns in cattle and antelopes have a centre made of bone. This sticks out from the skull. The bone is covered by a material called horn. A rhino horn is not made from bone. It develops from the skin and is made from fibres, like hair, which have become firmly stuck together.

Are the antlers of a deer made of bone?
Yes, they are. In most kinds of deer only the male deer grows antlers. There are two exceptions. In the reindeer and the caribou both males and females have antlers. A deer grows antlers each summer and sheds them in the winter or early spring. When the antlers are fully grown the tubes which supply them with blood close. When the deer sheds antlers there is no blood lost.

Is an elephant's tusk made from bone?
No. It is a tooth. The tooth is an incisor tooth that grows in the upper jaw. The incisor teeth in your upper jaw are the four teeth right at the front which people see straight away when you smile. Imagine two of them becoming tusks, which stick out a metre or so from your face.