| sagittal axis | In dentistry, the line in the frontal plane around which the working side condyle rotates during mandibular movement. (05 Mar 2000) |
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| principal optic axis | A line passing through the centre of the lens of a refracting system at right angles to its surface. (05 Mar 2000) |
| Helmholtz' axis ligament | <anatomy> A ligament forming the axis about which the malleus rotates; it consists of two portions extending from the anterior and the posterior border, respectively, of the tympanic notch to the malleus. Synonym: axis ligament of malleus. (05 Mar 2000) |
| hinge axis | An imaginary line around which the mandible may rotate through the horizontal plane. Synonym: hinge axis, mandibular axis. (05 Mar 2000) |
| secondary axis | Any ray passing through the optical centre of a lens. (05 Mar 2000) |
| pupillary axis | A line perpendicular to the surface of the cornea, passing through the centre of the pupil; the "direction of gaze." (05 Mar 2000) |
| neural axis | The central nervous system; the brain and spinal cord. Synonym: encephalomyelonic axis, neural axis. (05 Mar 2000) |
| neutral axis of straight beam | The axis perpendicular to the plane of loading of a beam at stresses within the proportional limit; it lies at the gravity axis of the cross-section of the beam. (05 Mar 2000) |
| normal electrical axis | A mean electrical axis of the heart situated between -30 |
| symmetry axis | <radiobiology> The straight line (usually vertical) through the centre of a configuration, when the configuration is symmetric to all (axisymmetric, like the tokamak) or some (periodic, like the stellarator) rotations about this line. Usually the z-axis. (09 Oct 1997) |
| instantaneous electrical axis | The resultant axis of the electromotive forces developing in the heart at any given moment. (05 Mar 2000) |
| internal axis of eye | <anatomy> That part of the optic axis from the midpoint of the posterior surface of the cornea to the anterior surface of the retina opposite the posterior pole. Synonym: axis bulbi internus. (05 Mar 2000) |
| opening axis | An imaginary line around which the mandibular condyles may rotate during opening and closing movements. Compare: fulcrum line. (05 Mar 2000) |
| optical axis | <physics> The line passing through both the centres of curvature of the optical surfaces of a lens, the optical centreline for all the centres of a lens system. (09 Oct 1997) |
| optic axis | The axis of the eye connecting the anterior and posterior poles; it usually diverges from the visual axis by five degrees or more. Synonym: axis opticus. (05 Mar 2000) |