| longitudinal sinus | See: inferior sagittal sinus, superior sagittal sinus. Longitudinal vertebral venous sinus, large, plexiform veins forming portions of the anterior internal vertebral venous plexus lying on the posterior surfaces of the vertebral bodies on either side of the posterior longitudinal ligament. Synonym: sinus vertebrales longitudinales. Luschka's sinus, venous sinus in the petrosquamous suture. (05 Mar 2000) |
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| longitudinal studies | Studies in which variables relating to an individual or group of individuals are assessed over a period of time. (12 Dec 1998) |
| longitudinal study | <epidemiology> A study taking place over time. If individuals are followed, this is a longitudinal cohort study. If individuals are not followed, but classes (usually age classes) are restudied, this is a longitudinal cross-sectional study. The converse of a horizontal study. (05 Dec 1998) |
| longitudinal sulcus of heart | See: anterior interventricular groove, posterior interventricular groove. (05 Mar 2000) |
| longitudinal wave | <physics> Waves where the variation of the field is partially or totally in the direction of propagation (parallel to wavennumber, k [a vector]). Examples include sound waves and Langmuir waves. Contrasted with transverse waves, where the variation is perpendicular to the direction of propagation, such as light waves. (13 Nov 1997) |
| abdominothoracic arch | A bell-shaped line defined by the lower end of the sternum and the costal arches on each side, constituting a boundary line between the anterolateral portions of the thoracic and abdominal walls. (05 Mar 2000) |
| alveolar arch of mandible | The free margin of the alveolar process of the mandible. Synonym: arcus alveolaris mandibulae, limbus alveolaris. (05 Mar 2000) |
| alveolar arch of maxilla | The free border of the alveolar process of the maxilla. Synonym: arcus alveolaris maxillae, limbus alveolaris. (05 Mar 2000) |
| anterior arch of atlas | 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) |
| anterior palatine arch | One of a pair of ridges or folds of mucous membrane passing from the soft palate to the side of the tongue; it encloses the palatoglossus muscle and forms anterior margin of the tonsillar fossa. Also demarcates oral cavity from isthmus of fauces. Synonym: arcus palatoglossus, anterior palatine arch, anterior pillar of fauces, arcus glossopalatinus, glossopalatine arch, glossopalatine fold. (05 Mar 2000) |
| aortic arch | The curved portion between the ascending and descending parts of the aorta; it begins as a continuation of the ascending aorta posterior to the sternal angle, runs posteriorly and slightly to the left as it passes over the root of the left lung, and becomes the descending aorta as it reaches and begins to course along the vertebral column; it gives rise to the brachiocephalic trunk, the left common carotid and left subclavian arteries. Any member of the several pairs of arterial channels encircling the embryonic pharynx in the mesenchyme of the brachial arches; there are potentially six pairs, but in mammals the fifth pair is poorly developed or absent. The first and second pairs are functional only in very young embryos; the third pair is involved in the formation of the carotids; the fourth arch on the left is incorporated in the arch of the aorta; the sixth pair forms the proximal part of the pulmonary arteries. A series of arterial channels encircling the embryonic pharynx in the mesenchyme of the branchial arch's. There are potentially six pairs, but in mammals the fifth pair is poorly developed or absent. The first and second pairs are functional only in very young embryos; the third pair is involved in the formation of the carotids; the fourth arch on the left is incorporated in the arch of the aorta; the sixth pair forms the proximal part of the pulmonary arteries. Synonym: arcus aortae. (05 Mar 2000) |
| aortic arch syndrome | <syndrome> Aortic arch syndrome, also referred to by many as vertebral-basilar artery disease, carotid artery occlusive syndrome and subclavian steal syndrome is characterised by a constellation of signs and symptoms which occur secondary to abnormalities in the major arteries which extend off of the aortic arch. These abnormalities are structural and most often secondary to the effects of atherosclerosis, blood clots, trauma or a congenital abnormality. Symptoms of this condition include various neurologic symptoms, reduction in pulse and changes in blood pressure. (27 Sep 1997) |
| aortic arch syndromes | Any of a group of disorders leading to occlusion of the arteries arising from the aortic arch. Such occlusion may be caused by atherosclerosis, arterial embolism, syphilitic or tuberculous arteritis, etc. (12 Dec 1998) |
| arch | <dentistry> Collectively, either the teeth or the basal bone of either jaw. (08 Jan 1998) |
| arch bar | Any one of several types of wires, bar's, or splints conforming to the arch of the teeth, extending from one side of the arch to the other and located labially, or lingually; used for the treatment of jaw fractures and/or stabilization of injured teeth. (05 Mar 2000) |