MU'COUS MEMBRANE. The thin layer of tissue which covers those internal cavities or pa.s.sages which communicate with the external air.

MU'CUS. The glairy fluid which is secreted by mucous membranes, and which serves to keep them in a moist condition.

MY-O'PI-A (Gr. [Greek: muo], _muo_, to contract, and [Greek: ops], _ops_, the eye). A defect of vision dependent upon an eyeball that is too long, rendering distant objects indistinct; near-sight.

NA'SAL (L. _na'sus_, the nose). Pertaining to the nose; the _nasal cavities_ contain the distribution of the special nerve of smell.

NERVE (Gr. [Greek: neuron], _neuron_, a cord or string). A glistening, white cord of cylindrical shape, connecting the brain or spinal cord with some other organ of the body.

NERVE CELL. A minute, round and ashen-gray cell found in the brain and other nervous centres.

NERVE FI'BRE. An exceedingly slender thread of nervous tissue found in the various nervous organs, but especially in the nerves; it is of a white color.

NU-TRI'TION (L. _nu'trio_, to nourish). The processes by which the nourishment of the body is accomplished.

OE-SOPH'A-GUS (Gr.). Literally, that which carries food. The tube leading from the throat to the stomach; the gullet.

O-LE-AG'I-NOUS (L. _o'leum_, oil). Of the nature of oil: applied to an important group of food-principles--the fats.

OL-FAC'TO-RY (L. _olfa'cio_, to smell). Pertaining to the sense of smell.

OPH-THAL'MO-SCOPE (Gr. [Greek: ophthalmos], _ophthalmos_, the eye, and [Greek: skopeo], _skopeo_, to look at). An instrument devised for examining the interior of the globe of the eye.

OP'TIC (Gr. [Greek: opto], _opto_, to see). Pertaining to the sense of sight.

OR'BIT (L. _or'bis_, the socket). The bony socket or cavity in which the eyeball is situated.

OS'MOSE (Gr. [Greek: osmos], _osmos_, a thrusting or impulsion). The process by which liquids are impelled through a moist membrane.

OS'SE-OUS (L. _os_, a bone). Consisting of, or resembling bone.

PAL'ATE (L. _pala'tum_, the palate). The roof of the mouth, consisting of the hard and soft palate.

{260} PAL'MAR. Relating to the palm of the hand.

PAN'CRE-AS (Gr. [Greek: pas], [Greek: pantos], _pas_, _pantos_, all, and [Greek: kreas], _kreas_, flesh). A long, flat gland situated near the stomach; in the lower animals the a.n.a.logous organ is called the sweet-bread.

PA-PIL'Lae (L. _papil'la_). The minute prominences in which terminate the ultimate fibres of the nerves of touch and taste.

PA-RAL'Y-SIS. A disease of the nervous system marked by the loss of sensation, or voluntary motion, or both; palsy.

PAR-A-PLE'GI-A (Gr. [Greek: paraplesso], _paraplesso_, to strike amiss). A form of paralysis affecting the lower half of the body.

PA-TEL'LA (L. dim. of _pat'ina_, a pan). The knee-pan; a small bone.

PEL'VIS (L.). Literally a basin; the bony cavity at the lower part of the trunk.

PEP'SIN (Gr. [Greek: pepto], _pepto_, to digest). The organic principle of the gastric juice.

PER-I-STAL'TIC MOVE'MENTS (Gr. [Greek: peristello], _peristello_, to contract). The slow, wave-like movements of the stomach and intestines.

PER-I-TO-NE'UM (Gr. [Greek: periteino], _periteino_, to stretch around).

The investing membrane of the stomach, intestines, and other abdominal organs.

PER-SPI-RA'TION (L. _perspi'ro_, to breathe through). The sweat, or watery exhalation of the skin; when visible, it is called _sensible_ perspiration, when invisible, it is called _insensible_ perspiration.

PE'TROUS (Gr. [Greek: petra], _petra_, a rock). The name of the hard portion of the temporal bone, in which is situated the drum of the ear and labyrinth.

PHAR'YNX (Gr. [Greek: pharunx], _pharunx_, the throat). The cavity between the back of the mouth and gullet.

PHYS-I-OL'O-GY (Gr. [Greek: phusis], _phusis_, nature, and [Greek: logos], _logos_, a discourse). The science of the functions of living, organized beings.

PI'A MA'TER (L.). Literally, the tender mother; the innermost of the three coverings of the brain. It is thin and delicate; hence the name.

PLEU'RA (Gr. [Greek: pleura], a rib). A membrane covering the lung and lining the chest. There is one for each lung.

PLEU'RI-SY. An inflammation affecting the pleura.

PNEU-MO-GAS'TRIC (Gr. [Greek: pneumon], _pneumon_, the lungs, and [Greek: gaster], _gaster_, the stomach). The name of a nerve distributed to the lungs and stomach; it is the princ.i.p.al nerve of respiration.

PNEU-MO'NIA (Gr.). An inflammation affecting the air-cells of the lungs.

{261} PRES-BY-O'PI-A (Gr. [Greek: presbus], _presbus_, old, and [Greek: ops], _ops_, the eye). A defect of the accommodation of the eye, caused by the hardening of the crystalline lens; the "far-sight" of adults and aged persons.

PROC'ESS (L. _proce'do_, _proces'sus_, to proceed, to go forth). Any projection from a surface. Also, a method of performance; a procedure.

PTY'A-LIN (Gr. [Greek: ptualon], _ptualon_, saliva). The peculiar organic ingredient of the saliva.

PUL'MO-NA-RY (L. _pul'mo_, _pulmo'nis_, the lungs). Pertaining to the lungs.

PULSE (L. _pel'lo_, _pul'sum_, to beat). The striking of an artery against the finger, occasioned by the contraction of the heart, commonly felt at the wrist.

PU'PIL (L. _pupil'la_). The central, round opening in the iris, through which light pa.s.ses into the depths of the eye.

PY-LO'RUS (Gr. [Greek: puloros], _puloros_, a gate-keeper). The lower opening of the stomach, at the beginning of the small intestine.

RE'FLEX ACTION. An involuntary action of the nervous system, by which an external impression conducted by a sensory nerve is reflected, or converted into a motor impulse.

RES-PI-RA'TION (L. _res'piro_, to breathe frequently). The function of breathing, comprising two acts: _inspiration_, or breathing in, and _expiration_, or breathing out.

RET'I-NA (L. _re'te_, a net). The innermost of the three tunics or coats of the eyeball, being an expansion of the optic nerve.

SAC'CHA-RINE (L. _sac'charum_, sugar). Of the nature of sugar; applied to the important group of food substances which embraces the different varieties of sugar, starch, and gum.

SA-LI'VA (L.). The moisture or fluids of the mouth, secreted by the salivary glands, etc.

SCLE-ROT'IC (Gr. [Greek: skleros], _skleros_, hard). The tough, fibrous outer tunic of the eyeball.

SE-BA'CEOUS (L. _seb.u.m_, fat). Resembling fat, the name of the oily secretion by which the skin is kept flexible and soft.