| mastoid fossa | A small depression on the mastoid part of the temporal bone, posterior to the suprameatal spine. Synonym: foveola suprameatica, mastoid fossa, fossa mastoidea, supramastoid fossa. (05 Mar 2000) |
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| mastoid groove | The groove medial to the mastoid process of the temporal bone from which the digastric muscle originates. Synonym: incisura mastoidea, digastric groove, digastric notch, mastoid notch. (05 Mar 2000) |
| mastoid lymph nodes | Two or three nodes in the region of the mastoid process; they receive afferent lymphatic vessels from the scalp and auricle and send efferent vessels to the superior deep cervical nodes. Synonym: nodi lymphatici mastoidei, mastoid lymph nodes. (05 Mar 2000) |
| mastoid margin of occipital bone | The margin of the occipital squama that articulates with the temporal bone. Synonym: margo mastoideus squamae occipitalis, mastoid margin of occipital bone. (05 Mar 2000) |
| mastoid notch | The groove medial to the mastoid process of the temporal bone from which the digastric muscle originates. Synonym: incisura mastoidea, digastric groove, digastric notch, mastoid notch. (05 Mar 2000) |
| mastoid part of the temporal bone | The portion of the petrous part of the temporal bone bearing the mastoid process. Synonym: pars mastoidea ossis temporalis. (05 Mar 2000) |
| mastoid process | The nipple-like projection of the petrous part of the temporal bone. Synonym: processus mastoideus, mastoid bone, temporal apophysis. (05 Mar 2000) |
| mastoid sinuses | Numerous small intercommunicating cavities in the mastoid process of the temporal bone that empty into the mastoid or tympanic antrum. Synonym: cellulae mastoideae, mastoid cells, mastoid sinuses. (05 Mar 2000) |
| mastoid wall of middle ear | It contains the opening into the mastoid antrum. Synonym: paries mastoideus cavi tympani, mastoid wall of middle ear, posterior wall of middle ear. (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) |