| parallel rays | Ray's parallel to the axis of an optical system. (05 Mar 2000) |
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| parallel track | <pharmacology> A system for distributing certain experimental drugs to people who are unable to participate in ongoing clinical trials. (09 Oct 1997) |
| plane-parallel | <optics> Having opposite surfaces exactly plane and parallel, as a piece of glass. Source: Websters Dictionary (01 Mar 1998) |
| 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) |
| 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) |
| 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) |