| BSL | benign symmetric lipomatosis; blood sugar level |
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| MSL | midsternal line; multiple symmetric lipomatosis |
| SCBG | symmetric calcification of the basal cerebral ganglia |
| STNR | symmetric tonic neck reflex |
| second parallel pelvic plane | The plane extending from the middle of the posterior surface of the pubic symphysis to the junction of the second and third sacral vertebrae, and laterally passing through the ischial bones over the middle of the acetabulum. Synonym: second parallel pelvic plane, wide plane. (05 Mar 2000) |
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| dizygotic twin | <embryology> Twins which are the result of two separate zygotes, or two separate eggs fertilized by two separate sperm. They can be any combination of sexes (two males, two females, one of each). Compare: monozygotic twins. (09 Oct 1997) |
| 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) |
| twin | 1. Being one of two born at a birth; as, a twin brother or sister. 2. Being one of a pair much resembling one another; standing the relation of a twin to something else; often followed by to or with. 3. <botany> Double; consisting of two similar and corresponding parts. 4. <chemistry> Composed of parts united according to some definite law of twinning. See Twin. Twin boat, or Twin ship, a vessel whose deck and upper works rest on two parallel hulls. Twin crystal. See Twin. <botany> Twin flower, a delicate evergreen plant (Linnaea borealis) of northern climates, which has pretty, fragrant, pendulous flowers borne in pairs on a slender stalk. Twin-screw steamer, a steam vessel propelled by two screws, one on either side of the plane of the keel. Origin: OE. Twin double, AS. Getwinne two and two, pl, twins; akin to D. Tweeling a twin, G. Zwilling, OHG. Zwiniling, Icel. Tvennr, tvinnr, two and two, twin, and to AS. Twi- two. See Twice, Two. 1. One of two produced at a birth, especially by an animal that ordinarily brings forth but one at a birth; used chiefly in the plural, and applied to the young of beasts as well as to human young. 2. <astronomy> A sign and constellation of the zodiac; Gemini. See Gemini. 3. A person or thing that closely resembles another. 4. <chemistry> A compound crystal composed of two or more crystals, or parts of crystals, in reversed position with reference to each other. The relative position of the parts of a twin may be explained by supposing one part to be revolved 180 deg about a certain axis (called the twinning axis), this axis being normal to a plane (called the twinning plane) which is usually one of the fundamental planes of the crystal. This revolution brings the two parts into parallel position, or vice versa. A contact twin is one in which the parts are united by a plane surface, called the composition face, which is usually the same as the twinning plane. A penetration twin is one in which the parts interpenetrate each other, often very irregularly. Twins are also called, according to form, cruciform, geniculated, etc. Source: Websters Dictionary (01 Mar 1998) |
| twin cone | Two retinal cone's fused together. (05 Mar 2000) |
| twin crystal | Two crystal's that have grown together along a common face. (05 Mar 2000) |
| twin helix | The helical structure assumed by two strands of deoxyribonucleic acid, held together throughout their length by hydrogen bonds between bases on opposite strands, referred to as Watson-Crick base pairing. See: base pair. Synonym: DNA helix, double helix, twin helix. (05 Mar 2000) |
| twin method | A general means of genetic analysis that capitalises on the fact that while twins have the same age and the same intrauterine environment, identical (monozygotic) twins have the same genotype but dizygotic twins are no more alike than sibs and may be of different sex. (05 Mar 2000) |
| twin placenta | The placenta(s) of a twin pregnancy; if dizygotic, the placenta's may be separate or fused, the latter retaining two amniotic and two chorionic sacs (dichorionic diamniotic placenta); if monozygotic, the placenta may be a (05 Mar 2000) |
| twin pregnancy | A pregnancy that may result from the fertilization of two separate ova or of a single ovum. See: twin. Synonym: bigeminal pregnancy. (05 Mar 2000) |
| twin studies | Methods of detecting genetic aetiology in human traits. The basic premise of twin studies is that monozygotic twins, being formed by the division of a single fertilised ovum, carry identical genes, while dizygotic twins, being formed by the fertilization of two ova by two different spermatozoa, are genetically no more similar than two siblings born after separate pregnancies. (12 Dec 1998) |
| twin study | A method of detecting genetic causes in human traits and genetic factors in behaviour using sets of twins. (12 Dec 1998) |
| extinction parallel | <microscopy> Vibration directions parallel and perpendicular to the long direction of the crystal or fibre. (05 Aug 1998) |
| first parallel pelvic plane | The upper opening of the true pelvis, bounded anteriorly by the pubic symphysis and the pubic crest on either side, laterally by the iliopectineal lines, and posteriorly by the promontory of the sacrum. Synonym: apertura pelvis superior, aditus pelvis, first parallel pelvic plane, pelvic brim, pelvic inlet, pelvic plane of inlet, plane of inlet. (05 Mar 2000) |
| fourth parallel pelvic plane | The lower opening of the true pelvis, bounded anteriorly by the pubic arch, laterally by the rami of the ischium and the sacrotuberous ligament on either side, and posteriorly by these ligaments and the tip of the coccyx. Synonym: apertura pelvis inferior, apertura pelvis minoris, fourth parallel pelvic plane, pelvic outlet, pelvic plane of outlet, plane of outlet. (05 Mar 2000) |