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mammal
A member of the class Mammalia. Mammals are warm-blooded, usually hairy vertebrates whose offspring are fed with milk secreted by the mammary glands. All but a few are placental (see placenta). About 4,000 living species are known, including humans and their main domestic animals. The mammals are divided into three subclasses: the Monotremata (monotremes), Metatheria (marsupials), and the Eutheria (placental mammals).
In mammals, the bones and muscles of the legs carry the weight of the body, while the backbone is a girder between them from which the gut and other organs hand. The rib-cage protects the lungs and heart, but an important difference between mammals and birds is the separation of these organs from the organs in the lower part of the body by a thin sheet of muscle – the diaphragm.
The brain is more developed in mammals than in any other group, allowing for the variety of activities that is characteristic of them.
Most mammals give birth to their young alive (the monotremes, such as the platypus and spiny anteater, which lay eggs, are an exception); structures occur in the female therefore that are not found in birds and reptiles. In marsupials the young are born at a very early stage and suckled in a pouch. The latter is supported by the so-called epipubic bones. These are not found in other mammals.
Mammalian teeth are usually of several kinds – specialized for grinding, tearing flesh, and so on.
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• ZOOLOGY
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