Tartar. A hard crust which forms on the teeth, and is composed of salivary mucus, animal matter, and a compound of lime. Temporal (Lat. _tempus_, time, and _tempora_, the temples). Pertaining to the temples; so called because the hair begins to turn white with age in that portion of the scalp. Tendon (Lat. _tendo_, to stretch). The white, fibrous cord, or band, by which a muscle is attached to a bone; a sinew. Tetanus (Gr. τείνω, to stretch). A disease marked by persistent contractions of all or some of the voluntary muscles; those of the jaw are sometimes solely affected; the disorder is then termed lockjaw. Thorax (Gr. θώραξ, a breast-plate). The upper cavity of the trunk of the body, containing the lungs, heart, etc.; the chest. Thyroid (Gr. εἶδος, a shield, and εἶ̓δος, form). The largest of the cartilages of the larynx: its projection in front is called “Adam’s Apple.” Tissue. Any substance or texture in the body formed of various elements, such as cells, fibers, blood-vessels, etc., interwoven with each other. Tobacco (Indian _tabaco_, the tube, or pipe, in which the Indians smoked the plant). A plant used for smoking and chewing, and in snuff. Trachea (Gr. τραχύς, rough). The windpipe. Tragus (Gr. τράγος, a goat). The eminence in front of the opening of the ear; sometimes hairy, like a goat’s beard. Transfusion (Lat. _transfundo_, to pour from one vessel to another). The operation of injecting blood taken from one person into the veins of another. Trichina Spiralis. (A twisted hair). A minute species of parasite, or worm, which infests the flesh of the hog: may be introduced into the human system by eating pork not thoroughly cooked. Trochanter (Gr. τροχάω, to turn, to revolve). Name given to two projections on the upper extremities of the femur, which give attachment to the _rotator_ muscles of the thigh. Trypsin. The ferment principle in pancreatic juice, which converts proteid material into peptones. Tubercle (Lat. _tuber_, a bunch). A pimple, swelling, or tumor. A morbid product occurring in certain lung diseases. Tuberosity (Lat. _tuber, tuberis_, a swelling). A protuberance. Turbinated (Lat. _turbinatus_, from _turbo, turbinis_, a top). Formed like a _top_; a name given to the bones in the outer wall of the nasal fossæ. Tympanum (Gr. τύμπανον, a drum). The cavity of the middle ear, resembling a drum in being closed by two membranes. Umbilicus (Lat., the navel.) A round cicatrix or scar in the median line of the abdomen. Urea (Lat. _urina_, urine). Chief solid constitutent of _urine_. Nitrogenous product of tissue decomposition. Ureter (Gr. οὐρέω, to pass urine). The tube through which the _urine_ is conveyed from the kidneys to the bladder. Uvula (Lat. _uva_, a grape). The small, pendulous body attached to the back part of the palate. Vaccine Virus (Lat. _vacca_, a cow, and _virus_, poison). The material derived from heifers for the purpose of vaccination,—the great preventive of smallpox.