Membrane. A thin layer of tissue serving to cover some part of the body.
Mesentery (Gr. μέσος, middle, and ἔντερον, the intestine). A duplicature of the peritoneum covering the small intestine, which occupies the middle or center of the abdominal cavity.
Metabolism (Gr. μεταβολή, change). The changes taking place in cells, whereby they become more complex and contain more force, or less complex and contain less force. The former is constructive metabolism, or anabolism; the latter, destructive metabolism, or katabolism.
Microbe (Gr. μικρός, little, and βίος, life). A microscopic organism, particularly applied to bacteria.
Microscope (Gr. μικρός, small, and σκοπέω, to look at). An optical instrument which assists in the examination of minute objects.
Molar (Lat. mola, a mill). The name applied to the three back teeth at each side of the jaw; the grinders, or mill-like teeth.
Molecule (dim. of Lat. moles, a mass). The smallest quantity into which the mass of any substance can physically be divided. A molecule may be chemically separated into two or more atoms.
Morphology (Gr. μόρφη, form, and λόγος, discourse). The study of the laws of form or structure in living beings.
Motor (Lat. moveo, motum, to move). The name of the nerves which conduct to the muscles the stimulus which causes them to contract.
Mucous Membrane. The thin layer of tissue which covers those internal cavities or passages which communicate with the external air.