This section is from the book "The Home Cyclopedia Of General Information", by Charles Morris. Also available from Amazon: Home Cyclopedia of Necessary Knowledge.
[L. mamma.] The highest class of vertebrate or backboned animals; so called because they all feed their young with milk formed in their own bodies. In mammals the heart is divided into four chambers, the blood is warm, and the skin has a covering of hair, wool, or bristles.
 
Continue to: