| aperture function | <microscopy> In a diffraction-limited optical system, the function that determines the relationship between the image and each point in the object. Modifying the aperture function changes the image according to the modified Fourier-filtering (or optical filtration) property of the aperture. (05 Aug 1998) |
|---|---|
| aperture of mastoid antrum | The orifice leading from the epitympanic recess to the mastoid antrum. Synonym: aditus ad antrum. (05 Mar 2000) |
| aperture of orbit | The somewhat quadrangular anterior entrance to the orbit which forms the base of the pyramid-shaped orbital cavity. It is bounded by the sharp supra-, infra-, and lateral orbital margins and a less obvious medial margin on each side of the upper nose. Synonym: aditus orbitae, aperture of orbit. (05 Mar 2000) |
| aperture plane | <microscopy> In a microscope adjusted for Koehler illumination, the conjugate planes that include the light source, the condenser iris diaphragm, the objective lens back aperture, and the eye point. Spaces in the aperture planes are the reciprocal of those in the field planes. (05 Aug 1998) |
| aperture, angular | <microscopy> The angle between the most divergent rays that can pass through a lens to form the image of an object. The angle subtended between the axis of a lens and the largest accepted angle of the image-forming rays. With microscope objectives the trigonometric sine of this angle is used to define numerical aperture but as measured from the axial object point. (05 Aug 1998) |
| aperture, effective | <microscopy> The diameter of the entrance pupil: it is the apparent diameter of the limiting aperture measured from the front. (05 Aug 1998) |
| apetalous | <botany> Without petals. (09 Oct 1997) |
| apex | <dentistry> The very bottom of the root of your tooth. (08 Jan 1998) |
| apex auriculae | A point projecting upward and posteriorly from the free outcurved margin of the helix a little posterior to its upper end. Synonym: apex auriculae, apex satyri, Woolner's tip. (05 Mar 2000) |
| apex beat | The visible and/or palpable pulsation made by the apex of the left ventricle as it strikes the chest wall in systole; normally in the fifth intercostal space, about 10 cm to the left of the median line. (05 Mar 2000) |
| apex capitis fibulae | The pointed upper end of the fibular head to which is attached the arcuate popliteal ligament and part of the biceps femoris tendon. Synonym: apex capitis fibulae, styloid process of fibula. (05 Mar 2000) |
| apex cartilaginis arytenoideae | The pointed upper end of the cartilage which supports the corniculate cartilage and the aryepiglottic fold. Synonym: apex cartilaginis arytenoideae. (05 Mar 2000) |
| apex cordis | The blunt extremity of the heart formed by the left ventricle. See: apex beat. Synonym: apex cordis, vertex cordis. (05 Mar 2000) |
| apex cornus posterioris | The pointed extremity of each posterior gray column or cornu of the spinal cord. Synonym: apex cornus posterioris, caput cornus, tip of posterior horn. (05 Mar 2000) |
| apex cuspidis dentis | The tip of the peaklike projections from the crown of a tooth. Synonym: apex cuspidis dentis. (05 Mar 2000) |