AN-ÆS-THET´ICS (Greek, [Greek: an], _an_, without, [Greek: aisthesia], _aisthesia_, feeling).--Those medicinal agents which prevent the feeling of pain, such as chloroform, laughing-gas, etc. AN-I-MAL´CULE (L. _animal´culum_, a small animal). Applied to animals which can only be seen with the aid of the microscope. Animalculum (plural, animalcula) is used with the same meaning. A-OR´TA (Gr. [Greek: aorteomai], _aorteomai_, to be lifted up). The largest artery of the body, and main trunk of all the arteries. It arises from the left ventricle of the heart. The name was first applied to the two large branches of the trachea, which appear to be lifted up by the heart. {253} A´QUE-OUS HUMOR (L. _aqua_, water). A few drops of watery colorless fluid occupying the space between the cornea and crystalline lens. A-RACH´NOID MEM´BRANE (Gr. [Greek: arachne], _arachne_, a cobweb, and [Greek: eidos], _eidos_, like). An extremely thin covering of the brain and spinal cord. It lies between the _dura mater_ and the _pia mater_. AR´BOR VI´TÆ (L.). Literally, "the tree of life;" a name given to the peculiar appearance presented by a section of the cerebellum. AR´TER-Y (Gr. [Greek: aer], _aer_, air, and [Greek: terein], _terein_, to contain). A vessel by which blood is conveyed away from the heart. It was supposed by the ancients to contain air; hence the name. AR-TIC-U-LA´TION (L. _articulo_, to form a joint). The more or less movable union of bones, etc.; a joint. A-RYT´E-NOID CAR´TI-LA-GES (Gr. [Greek: arutaina], _arutaina_, a pitcher). Two small cartilages of the larynx, resembling the mouth of a pitcher. AS-SIM-I-LA´TION (L. _ad_, to, and _similis_, like). The conversion of food into living tissue. AU-DI´TION (L. _audio_, to hear). The act of hearing sounds. AU´DI-TO-RY NERVE. One of the cranial nerves; it is the special nerve of hearing. AU´RI-CLE (L. _auris_, the ear). A cavity of the heart. BAR´I-TONE (Gr. [Greek: barus], _barus_, heavy, and [Greek: tonos], _tonos_, tone). A variety of male voice between the bass and tenor. BEL-LA-DON´NA (It. beautiful lady). A vegetable narcotic poison. It has the property of enlarging the pupil, and thus increasing the brilliancy of the eye; so called from its use by Italian ladies. BI-CUS´PID (L. _bi_, two, and _cuspis_, prominence). The name of the fourth and fifth teeth on each side of the jaw; possessing two prominences. BILE. The gall, or peculiar secretion of the liver; a viscid, yellowish fluid, and very bitter to the taste. BRONCH´I (Gr. [Greek: bronkos], _bronkos_, the windpipe). The two first divisions or branches of the trachea; one enters each lung. BRONCH´I-AL TUBES. The smaller branches of the trachea within the substance of the lungs, terminating in the air-cells. BRONCH-I´TIS (from _bronchia_, and _itis_, a suffix signifying inflammation). An inflammation of the larger bronchial tubes; a "cold" affecting the lungs. CAL-CA´RE-OUS (L. _calx_, lime). Containing lime.