Hypertrophy (Gr. ?p??, over, and t??f?, nourishment). Excessive growth; thickening or enlargement of any part or organ.

Incisor (Lat. _incido_, to cut). Applied to the four front teeth of both jaws, which have sharp, cutting edges.

Incus. An anvil; the name of one of the bones of the middle ear.

Indian Hemp. The common name of _Cannabis Indica_, an intoxicating drug known as _hasheesh_ and by other names in Eastern countries.

Inferior Vena Cava. The chief vein of the lower part of the body.

Inflammation (Lat. prefix _in_ and _flammo_, to flame). A redness or swelling of any part of the body with heat and pain.

Insalivation (Lat. _in_ and _saliva_, the fluid of the mouth). The mingling of the saliva with the food during the act of chewing.

Inspiration (Lat. _inspiro, spiratum_, to breathe in). The act of drawing in the breath.

Intestine (Lat. _intus_, within). The part of the alimentary ca.n.a.l which is continuous with the lower end of the stomach; also called the bowels.

Iris (Lat. _iris_, the rainbow). The thin, muscular ring which lies between the cornea and crystalline lens, giving the eye its special color.

Jaundice (Fr. _jaunisse_, yellow). A disorder in which the skin and eyes a.s.sume a yellowish tint.

Katabolism (Gr. ?ata????, to throw down). The process by means of which the more complex elements are rendered more simple and less complex. The opposite of _anabolism_.

Labyrinth. The internal ear, so named from its many windings.

Lacrymal Apparatus (Lat. _lacryma_, a tear). The organs for forming and carrying away the tears.

Lacteals (Lat. _lac, lactis_, milk). The absorbent vessels of the small intestines.

Laryngoscope (Gr. ??????, larynx, and s??p??, to behold). An instrument consisting of a mirror held in the throat, and a reflector to throw light on it, by which the interior of the larynx is brought into view.

Larynx. The cartilaginous tube situated at the top of the windpipe.

Lens. Literally, a lentil; a piece of transparent gla.s.s or other substance so shaped as either to converge or disperse the rays of light.

Ligament (Lat. _ligo_, to bind). A strong, fibrous material binding bones or other solid parts together.

Ligature (Lat. _ligo_, to bind). A thread of some material used in tying a cut or injured artery.

Lobe. A round, projecting part of an organ, as of the liver, lungs, or brain.

Lymph (Lat. _lympha_, pure water). The watery fluid conveyed by the lymphatic vessels.

Lymphatic Vessels. A system of absorbent vessels.

Malleus. Literally, the mallet; one of the small bones of the middle ear.

Marrow. The soft, fatty substance contained in the cavities of bones.

Mastication (Lat. _mastico_, to chew). The act of cutting and grinding the food to pieces by means of the teeth.

Meatus (Lat. _meo_, _meatum_, to pa.s.s). A _pa.s.sage_ or ca.n.a.l.

Medulla Oblongata. The "oblong marrow"; that portion of the brain which lies upon the basilar process of the occipital bone.

Meibomian. A term applied to the small glands between the conjunctiva and tarsal cartilages, discovered by _Meibomius_.

Membrana Tympani. Literally, the membrane of the drum; a delicate part.i.tion separating the outer from the middle ear; it is sometimes popularly called "the drum of the ear."

Membrane. A thin layer of tissue serving to cover some part of the body.

Mesentery (Gr. ?s??, middle, and ??te???, the intestine). A duplicature of the peritoneum covering the small _intestine_, which occupies the _middle_ or center of the abdominal cavity.

Metabolism (Gr. eta???, 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. ?????, little, and ???, life). A microscopic organism, particularly applied to bacteria.

Microscope (Gr. ?????, small, and s??p??;, to look at). An optical instrument which a.s.sists 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 ma.s.s). The smallest quant.i.ty into which the ma.s.s of any substance can physically be divided. A molecule may be chemically separated into two or more atoms.

Morphology (Gr. ??f?, form, and ?????, 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 pa.s.sages which communicate with the external air.

Mucus. The glairy fluid secreted by mucous membranes.

Myopia (Gr. ??, to shut, and ??, the eye). A defect of vision dependent upon an eyeball that is too long, rendering distant objects indistinct; _near sight_.

Myosin (Gr. ??, muscle). Chief proteid substance of muscle.

Narcotic (Gr. ?a????, to benumb). A medicine which, in poisonous doses, produces stupor, convulsions, and sometimes death.

Nerve Cell. A minute round and ashen-gray cell found in the brain and other nervous centers.

Nerve Fiber. An exceedingly slender thread of nervous tissue.

Nicotine. The poisonous and stupefying oil extracted from tobacco.