| back-action plugger | An instrument for condensing gold foil or amalgam in areas that cannot be reached directly. (05 Mar 2000) |
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| back aperture | <microscopy> The exit pupil of a microscope objective lens. The objective lens back aperture, which can be examined with a phase telescope or by inserting a Bertrand lens, displays the conoscopic interference figure and diffraction patterns. (05 Aug 1998) |
| back cross | <genetics> A crossing of a heterozygous organism and one of its homozygous parents. (09 Oct 1997) |
| back focal length | <microscopy> As measured on the principal axis, from the second lens vertex to the back focal point of the lens. It is not the equivalent of the focal length. (05 Aug 1998) |
| back focal plane | <microscopy> The plane, normal to the lens axis, situated at the back focus of a lens. (05 Aug 1998) |
| back injuries | General or unspecified injuries to the posterior part of the trunk. It includes injuries to the muscles of the back. (12 Dec 1998) |
| back-knee | Hyperextension of the knee, the lower extremity having a forward curvature. Synonym: back-knee. (05 Mar 2000) |
| back lens | <physics> In any compound lens (a lens system composed of more than one lens element), the last lens through which the light passes is called the back lens. It may be a single simple lens, a doublet, or triplet. See: front lens (05 Aug 1998) |
| back mutation | <molecular biology> A mutation that causes a mutant gene to revert to its original wild-type base sequence. Compare: forward mutation. (09 Oct 1997) |
| back of foot reflex | The foot being firmly supported on its inner side, a sharp tap on the dorsal tendons causes extension of the second to the fifth toes. Synonym: back of foot reflex, dorsum of foot reflex. (05 Mar 2000) |
| back pressure | Pressure exerted upstream in the circulation as a result of obstruction to forward flow, as when congestion in the pulmonary circulation results from stenosis of the mitral valve or failure of the left ventricle. (05 Mar 2000) |
| back-pressure renal atrophy | <radiology> Caliectasis without obstruction, due to repeated episodes of obstruction, gradual loss of renal pyramids (12 Dec 1998) |
| back teeth | All teeth posterior to the canines. (05 Mar 2000) |
| broadest muscle of back | <anatomy, muscle> Origin, spinous processes of lower five or six thoracic and the lumbar vertebrae, median ridge of sacrum, and outer lip of iliac crest; insertion, with teres major into posterior lip of bicipital groove of humerus; action, adducts arm, rotates it medially, and extends it; nerve supply, thoracodorsal. Synonym: musculus latissimus dorsi, broadest muscle of back. (05 Mar 2000) |
| regions of back | The topographical regions of the back of the trunk, including the vertebral region, sacral region, scapular region, infrascapular region, and lumbar region. Synonym: regiones dorsales. (05 Mar 2000) |