| third | 1. Next after the second; coming after two others; the ordinal of three; as, the thirdhour in the day. "The third night." 2. Constituting or being one of three equal parts into which anything is divided; as, the third part of a day. Third estate. In England, the commons, or the commonalty, who are represented in Parliament by the House of Commons. In France, the tiers etat. See Tiers etat. Third order See Third. Origin: OE. Thirde, AS. Ridda, fr. Ri, reo, three; akin to D. Derde third, G. Dritte, Icel. Rii, Goth. Ridja, L. Tertius, Gr, Skr. Ttiya. See Three, and cf. Riding a jurisdiction, Tierce. Source: Websters Dictionary (01 Mar 1998) |
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| third and fourth pharyngeal pouch syndrome | <syndrome> Also called the digeorge syndrome (dgs), this disorder is characterised by (1) low blood calcium levels (hypocalcaemia) due to underdevelopment (hypoplasia) of the parathyroid glands which control calcium; (2) underdevelopment (hypoplasia) of the thymus, an organ behind the breastbone in which lymphocytes mature and multiply; and (3) defects of the heart involving the outflow tracts more than from the heart. most cases of dgs are due to a microdeletion in chromosome band 22q11.2. A small number of cases have defects in other chromosomes, notably 10p13. Named after the american paediatric endocrinologist angelo digeorge. Another name for dgs is hypoplasia of the thymus and parathyroids. (12 Dec 1998) |
| third corpuscle | <haematology> A discoid cell (3m diameter) found in large numbers in blood, important for blood coagulation and for haemostasis by repairing breaches (small breaks) in the walls of blood vessels. Platelet _ granules contain lysosomal enzymes, dense granules contain ADP (a potent platelet aggregating factor) and serotonin (a vasoactive amine). They also release platelet-derived growth factor which presumably contributes to later repair processes by stimulating fibroblast proliferation. Synonym: thrombocytes. (09 Oct 1997) |
| third cranial nerve | <anatomy, nerve> Responsible for motor enervation of upper eyelid muscle, extraocular muscle and pupillary muscle. Lesions of the oculomotor nerve results in ptosis (dropping eyelid), deviation of the eyeball outward, double vision and a dilated pupil. (27 Sep 1997) |
| third degree burn | A burn involving destruction of the entire skin; deep third-degree burns extend into subcutaneous fat, muscle, or bone and often cause much scarring. Synonym: full-thickness burn. (05 Mar 2000) |
| third disease | <disease, virology> An acute, usually benign, infectious disease caused by a togavirus and most often affecting children and nonimmune young adults, in which the virus enters the respiratory tract via droplet nuclei and spreads to the lymphatic system. It is characterised by a slight cold, sore throat and fever, followed by enlargement of the postauricular, suboccipital and cervical lymph nodes and the appearances of a fine pink rash that begins on the head and spreads to become generalised. Synonym: German measles, rubeola. Origin: L. Rubellus = reddish, ruber = red (17 Dec 1997) |
| third eyelid | The semilunar fold formed by the palpebral conjunctiva at the medial angle of the eye, a fold of the conjunctival mucous membrane found in many animals; normally partially hidden in the medial canthus of the eye when at rest, it may be extended to cover part or all of the cornea in a winking-like action to clean the cornea, as in birds. Synonym: membrana nictitans, nictitating membrane, palpebra III, palpebra tertia, third eyelid. Synonym: plica lunata, plica semilunaris of eye, semilunar conjunctival fold. (05 Mar 2000) |
| third finger | Third finger. Synonym: digitus medius, digitus tertius, third finger. (05 Mar 2000) |
| third heart sound | Occurs in early diastole and corresponds with the end of the first phase of rapid ventricular filling; normal in children and younger people but abnormal in others. Synonym: third sound. (05 Mar 2000) |
| third law of thermodynamics | <chemistry> The entropy of a perfect crystal at 0 K is zero. (09 Jan 1998) |
| third molar | Eighth permanent tooth in the maxilla and mandible on each side, making it the most posterior tooth in human dentition; usually erupts between the seventeenth and twenty-third years; the roots are often fused, the separation being marked only by grooves; because it tends to erupt in an anterosuperior direction, the lower third molar often becomes impacted against the lower second molar; it is common for one or more third molar to fail to develop. Synonym: dens serotinus, molaris tertius, dens sapientiae, wisdom tooth. (05 Mar 2000) |
| third occipital nerve | <anatomy, nerve> Medial branch of the dorsal primary ramus of the third cervical nerve; this is usually joined with the greater occipital, but may exist as an independent nerve supplying cutaneous branches to the scalp and nucha. Synonym: nervus occipitalis tertius. (05 Mar 2000) |
| third-order kinetics | <pharmacology> A term describing the reaction rate of a chemical reaction in which the rate is proportional to the product of the concentrations (in moles) of three of the reactants, the product of the molar concentration of one reactant and the square of the molar concentration of another reactant, or the cube of the molar concentration of one of the reactants. Such a reaction might have an equation like rate = k[A][B][C] or rate = [A][B]2 or rate = [A]3, where k is the reaction rate constant, [A] is the concentration of reactant A, [B] is the concentration of reactant B, and [C] is the concentration of reactant C. (09 Oct 1997) |
| third ovary | An accessory ovary. (05 Mar 2000) |
| third parallel pelvic plane | The plane that extends from the end of the sacrum to the inferior border of the pubic symphysis; it is bounded posteriorly by the end of the sacrum, laterally by the ischial spines, and anteriorly by the inferior border of the pubic symphysis. Synonym: midplane, plane of least pelvic dimensions, plane of midpelvis, third parallel pelvic plane. (05 Mar 2000) |