| 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) |
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| 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) |
| third peroneal muscle | <anatomy, muscle> Origin, in common with musculus extensor digitorum longus; insertion, dorsum of base of fifth metatarsal bone; nerve supply, deep branch of peroneal; action, assists in dorsiflexion and eversion of foot. Synonym: musculus fibularis tertius, musculus peroneus tertius, third peroneal muscle. (05 Mar 2000) |
| third 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 stage of labour | The part of labour from the birth of the baby until the placenta (afterbirth) and foetal membranes are delivered. The third stage of labour is also called the placental stage. (12 Dec 1998) |
| third temporal convolution | A sagittal convolution on the inferolateral border of the temporal lobe of the cerebrum, separated from the middle temporal gyrus by the inferior temporal sulcus. On the inferior surface of the temporal lobe it is separated from the medial occipitotemporal gyrus by the occipitotemporal sulcus. It includes the lateral occipitotemporal gyrus. Synonym: gyrus temporalis inferior, inferior temporal convolution, third temporal convolution. (05 Mar 2000) |
| third tonsil | A collection of more or less closely aggregated lymphoid nodules on the posterior wall and roof of the nasopharynx, the hypertrophy of which constitutes the morbid condition called adenoids. Synonym: tonsilla pharyngealis, tonsilla adenoidea, Luschka's gland, Luschka's tonsil, third tonsil. (05 Mar 2000) |
| third trochanter | An occasional process at the proximal end of the lateral lip of the linea aspera of the femur, about on a level with the lesser trochanter, giving insertion to the greater part of the gluteus maximus muscle. See: gluteal tuberosity. (05 Mar 2000) |