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Movement on Land
Consider two vertebrates, the antelope and the lion. Both of these animals live on the African plains called the Savannah. The antelope is a herbivore, eating vegetation found on the savannah. Lions are carnivores and live in groups called prides. The female lions, the lionesses, do most of the hunting for the pride.
Lions eat many of the herbivores found on the African plains, including the antelope. Both of these animals need to be able to move fast. The antelope has to be able to run away from the lion. The lion has to be able to run faster than the antelope if it is going to catch it.
Antelope keep close together in groups. When there is any danger, the herd will start to run very quickly. The antelope will move one way and then another, and they make a lot of noise to try to confuse the lions.
The lions can only run fast for a short time. The lionesses creep silently towards the herd of antelope. They are the same colour as the dry savannah grass. This makes them well camouflaged and they are not noticed until the last moment. The lionesses get very close to the antelope before the herd starts to run. The lionesses now need to run as fast as they can. If they are successful they will catch one of the slower antelope, perhaps an old one which cannot move as fast as the others.
If the lionesses are unsuccessful in the first few minutes of their run they have to stop. They cannot run fast for a long time. They have to rest and try again later.
The lion and the antelope are both mammals. This means that they have a skeleton inside their bodies made of bone. This type of skeleton is called an endoskeleton (endo = inside)
The Vertebrate Skeleton
There are 206 bones in the adult human skeleton. The limbs (the arms and the legs) contain the longest bones. The longest of these bones is called the femur which is found in the thigh of the leg. A man who is 1,83 m tall has a 50 cm long femur. There are 27 bones in one hand and 21 different bones in the skull. The backbone has a total of 26 vertebrae.
Where two bones meet a joint is formed. A bone is too hard to move; it is impossible to bend bone! Bones can, however, change position at a joint. To allow this to happen muscles are attached to the bones. There are 100 joints in the human body and 639 different muscles.
When these muscles shorten (contract) the bones move closer to each other. Since all mammals have the same type of skeleton, we can study the human skeleton more closely and then compare it to the skeletons of the lion and the antelope.
There are four different types of joints in the human skeleton.
All of these joints can be found in the antelope and the antelope because they are both mammals. Both of these animals have powerful muscles in their back legs. This helps them to run fast. The big cats, such as the lion and the cheetah, have more flexible backbones than humans. This gives them longer strides when they run. using muscles, however, needs energy and these animals can not run fast for a long time.
The Arthropod Skeleton
The arthropods make up an invertebrate group. These animals have a skeleton on the outer surface of their bodies. This is called an exoskeleton (exo = outside). the exoskeleton is not made of bone but of a hard, flexible substance called chitin. The muscles are found inside the exoskeleton.