| piriform muscle | <anatomy, muscle> Origin, margins of pelvic sacral foramina and greater sciatic notch of ilium; insertion, upper border of greater trochanter; action, rotates thigh laterally; nerve supply, nerve to piriformis (sciatic plexus). Synonym: musculus piriformis, musculus pyriformis, piriform muscle. (05 Mar 2000) |
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| piriform neuron layer | The layer of Purkinje cells between the molecular and granular layers of the cerebellar cortex. Synonym: stratum neuronorum piriformium, ganglionic layer of cerebellar cortex, layer of piriform neurons, Purkinje's layer, stratum gangliosum cerebelli. (05 Mar 2000) |
| piriform opening | The anterior nasal opening in the skull. Synonym: apertura piriformis, piriform opening. (05 Mar 2000) |
| piriform recess | A recess in the anterolateral wall of the nasopharynx on each side of the vestible of the larynx separated from it by the aryepiglottic folds. Synonym: recessus piriformis, piriform recess, piriform sinus. (05 Mar 2000) |
| piriform sinus | A recess in the anterolateral wall of the nasopharynx on each side of the vestible of the larynx separated from it by the aryepiglottic folds. Synonym: recessus piriformis, piriform recess, piriform sinus. (05 Mar 2000) |
| layer of piriform neurons | The layer of Purkinje cells between the molecular and granular layers of the cerebellar cortex. Synonym: stratum neuronorum piriformium, ganglionic layer of cerebellar cortex, layer of piriform neurons, Purkinje's layer, stratum gangliosum cerebelli. (05 Mar 2000) |
| angle of aperture | <ophthalmology, optics> The angle formed by lines drawn from the ends of the diameter of a lens to its point of focus. See: angular aperture. (05 Mar 2000) |
| angular aperture | The angle, in air, of light that passes from the object to the ends of the diameter of the front lens of the microscope objective. (05 Mar 2000) |
| anterior nasal aperture | The anterior nasal opening in the skull. Synonym: apertura piriformis, piriform opening. (05 Mar 2000) |
| aperture | <physics> The opening in an optical system which restricts the size of the bundle of rays incident on a given surface. (Usually circular and specified by diameter.) (09 Oct 1997) |
| 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 correction | <microscopy> An electronic process used in some high-resolution video cameras and monitors that compensates for the loss in sharpness of detail due to the finite dimensions (aperture) of the scanning beam. (05 Aug 1998) |
| aperture diaphragm | A metal device that limits the area of the beam emerging from an X-ray tube. (05 Mar 2000) |
| 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) |
| aperture for electron microscopy | <technique> Anode aperture: The opening in the accelerating voltage anode shield of the electron gun through which the electrons must pass to irradiate the specimen. Condenser aperture: An opening in the condenser lens controlling the number of electrons entering the lens and the angular aperture of the electron beam. The angular aperture can also be controlled by the condenser lens current. Physical objective aperture: A metallic diaphragm, with a small central hole, used to limit the cone of electrons accepted by the objective lens. This improves image-contrast since highly scattered electrons are prevented from arriving at the Gaussian image plane and therefore cannot contribute to background fog. Aplanatic. Free from spherical aberration and coma. (05 Aug 1998) |