| ARAO | angiographic area of right anterior oblique projection |
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| ARV | acquired immunodeficiency syndrome-related virus; anterior right ventricle; avian reovirus |
| ASA | acetylsalicylic acid; active systemic anaphylaxis; Adams-Stokes attack; American Society of Anesthes... |
| asc | ascending; anterior subcapsular |
| ASIS | anterior superior iliac spine |
| anterior median line | The line of intersection of the midsagittal plane with the anterior surface of the body. Synonym: linea mediana anterior. (05 Mar 2000) |
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| anterior mediastinal arteries | <anatomy, artery> Small twigs supplying anterior mediastinal structures: mainly thymus and lymph nodes. Synonym: rami mediastinales arteriae thoracicae internae, rami thymici, anterior mediastinal arteries, arteriae thymicae, thymic arteries. (05 Mar 2000) |
| anterior mediastinal lymph nodes | Located in the superior mediastinum in relation to the great vessels, these nodes receive lymph from the thymus, pericardium and right side of the heart; their efferent vessels join those of the tracheal nodes to form the bronchomediastinal trunks. Synonym: nodi lymphatici mediastinales anteriores. (05 Mar 2000) |
| anterior mediastinotomy | A limited left anterior thoracostomy for biopsy of the mediastinal nodes out of reach by cervical mediastinoscopy. Synonym: anterior mediastinotomy. (05 Mar 2000) |
| anterior mediastinum | Anterior mediastinum, the narrow region between the pericardium and the sternum containing the thymus or its remnants, some lymph nodes and vessels and branches of the internal thoracic artery. Synonym: mediastinum anterius. (05 Mar 2000) |
| anterior medullary velum | The thin layer of white matter stretching between the two superior cerebellar peduncles, forming the roof of the superior recess of the fourth ventricle. Synonym: velum medullare superius, anterior medullary velum, Vieussens' valve. (05 Mar 2000) |
| anterior megalophthalmos | Congenital anomaly consisting of an enlarged anterior segment of the eye. Synonym: anterior megalophthalmos, megalocornea. Origin: kerato-+ L. Globus, ball (05 Mar 2000) |
| anterior meningeal artery | <anatomy, artery> Origin, anterior ethmoidal; distribution, meninges in anterior cranial fossa; anastomoses, branches of middle meningeal and meningeal branches of internal carotid and lacrimal. Synonym: arteria meningea anterior. (05 Mar 2000) |
| anterior meniscofemoral ligament | <anatomy> The ligamentous band that passes anterior to the posterior cruciate ligament, extending between the posterior portion of the lateral meniscus and the upper end of the anterior cruciate ligament. Synonym: ligamentum meniscofemorale anterius, Humphry's ligament. (05 Mar 2000) |
| anterior myocardial infarction | Infarction involving the anterior wall of the heart, and producing indicative electrocardiographic changes in the anterior chest leads and often in limb lead I. (05 Mar 2000) |
| anterior naris | 1. <anatomy> One of the external openings of the nose, which give passage to the air breathed and to secretions from the nose and eyes; one of the anterior nares. In sperm whales, porpoises, and allied animals, there is only one nostril, which is situated on the top of the head and called a spiracle. 2. Perception; insight; acuteness. "Methinks a man Of your sagacity and clear nostril should Have made another choice." (B. Jonson) Origin: OE. Nosethril, nosethirl, AS. Nospyrl; nos for nosu nose + pyrel opening, hole, from pyrel pierced, for pyrhel, fr. Purh through. See Nose, and Through, and cf. Thrill. Source: Websters Dictionary (01 Mar 1998) |
| anterior nasal aperture | The anterior nasal opening in the skull. Synonym: apertura piriformis, piriform opening. (05 Mar 2000) |
| anterior nasal spine | A pointed projection at the anterior extremity of the intermaxillary suture; the tip, as seen on a lateral cephalometric radiograph, is used as a cephalometric landmark. Synonym: spina nasalis anterior. (05 Mar 2000) |
| anterior neuropore | The temporary opening at the extreme rostral (cephalic) end of the early embryonic forebrain; closes at the 20th somite stage. Synonym: anterior neuropore, cranial neuropore. (05 Mar 2000) |
| anterior notch of cerebellum | A wide, shallow notch on the anterior surface of the cerebellum occupied laterally by the superior cerebellar peduncles and the inferior quadrigeminal bodies medially. Synonym: anterior notch of cerebellum, incisura cerebelli anterior, semilunar notch. (05 Mar 2000) |