Synopses & Reviews
Synopsis
Excerpt from The Standard Natural History, Vol. 5: Mammals
Like all vertebrates, the mammals never have more than two pairs of limbs, but with the exception of some of the aquatic forms (whale, these two pairs are always present, whence the name in frequent use for the class - quadrupeds. The anterior pair of limbs are never absent in the group. Except in a few forms, to be noted below, the body is covered with hair. The mouth is usually armed with teeth. The heart is four-chambered, and the circulation is complete. The blood is warm and contains non-nucleated red corpuscles. The body cavity is divided into two portions by a transverse muscle, the diaphragm, or midriff, the anterior portion being called the pleural, and the posterior, or abdominal portion, the peritoneal cavity. The young are born alive, and are afterward nourished by milk, secreted by milk glands (mammee), whence the name of the class.
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