| sinus aortae | The space between the superior aspect of each cusp of the aortic valve and the dilated portion of the wall of the ascending aorta, immediately above each cusp. Synonym: sinus aortae, Petit's sinus, Valsalva's sinus. Arlt's sinus, an inconstant depression on the lower portion of the internal surface of the lacrimal sac. Barber's pilonidal sinus, pilonidal sinus occurring in barbers, usually in the web between the fingers, due to the burying of exogenous hairs by the alternate loosening and tightening of tissues of the hand by the manipulation of scissors. (05 Mar 2000) |
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| isthmus aortae | A slight constriction of the aorta immediately distal to the left subclavian artery at the point of attachment of the ductus arteriosus. Synonym: isthmus aortae. (05 Mar 2000) |
| ostium aortae | The opening from the left ventricle into the ascending aorta; it is guarded by the aortic valve. Synonym: ostium aortae, aortic ostium. (05 Mar 2000) |
| arcus | Synonym: arch. Origin: L. A bow (05 Mar 2000) |
| arcus adiposus | An opaque, grayish ring at the periphery of the cornea just within the sclerocorneal junction, of frequent occurrence in the aged; it results from a deposit of fatty granules in, or hyaline degeneration of, the lamellae and cells of the cornea. Synonym: anterior embryotoxon, arcus adiposus, arcus juvenilis, arcus lipoides, arcus senilis, gerontoxon, linea corneae senilis, lipoidosis corneae. (05 Mar 2000) |
| arcus alveolaris mandibulae | The free margin of the alveolar process of the mandible. Synonym: arcus alveolaris mandibulae, limbus alveolaris. (05 Mar 2000) |
| arcus alveolaris maxillae | The free border of the alveolar process of the maxilla. Synonym: arcus alveolaris maxillae, limbus alveolaris. (05 Mar 2000) |
| arcus anterior atlantis | An arch that connects the lateral masses of the atlas anteriorly and articulates with the anterior articular facet of the dens of the axis. Synonym: arcus anterior atlantis. (05 Mar 2000) |
| arcus cartilaginis cricoideae | The narrow part of the cartilage that encircles the air passage anterior to the lamina. Synonym: arcus cartilaginis cricoideae. (05 Mar 2000) |
| arcus cornealis | An opaque, grayish ring at the periphery of the cornea just within the sclerocorneal junction, of frequent occurrence in the aged; it results from a deposit of fatty granules in, or hyaline degeneration of, the lamellae and cells of the cornea. Synonym: anterior embryotoxon, arcus adiposus, arcus juvenilis, arcus lipoides, arcus senilis, gerontoxon, linea corneae senilis, lipoidosis corneae. (05 Mar 2000) |
| arcus costalis | That portion of the inferior aperture of the thorax formed by the articulated cartilages of the seventh to tenth (false) ribs. Synonym: arcus costalis, arcus costarum. (05 Mar 2000) |
| arcus costarum | That portion of the inferior aperture of the thorax formed by the articulated cartilages of the seventh to tenth (false) ribs. Synonym: arcus costalis, arcus costarum. (05 Mar 2000) |
| arcus dentalis inferior | The teeth supported by the alveolar part of the mandible, whether the 10 deciduous teeth or the 16 permanent teeth. Synonym: arcus dentalis inferior, mandibular dentition. (05 Mar 2000) |
| arcus dentalis superior | The teeth supported by the alveolar process of the two maxillae, whether the 10 deciduous teeth or the 16 permanent teeth. Synonym: arcus dentalis superior, maxillary dentition. (05 Mar 2000) |
| arcus ductus thoracici | See: thoracic duct. (05 Mar 2000) |