| annulus umbilicalis | An opening in the linea alba through which pass the umbilical vessels in the foetus; in young embryos it is relatively nearer to the pubis, but gradually ascends to the centre of the abdomen; it is closed in the adult, its site being indicated by the umbilicus or navel. Synonym: annulus umbilicalis, canalis umbilicalis. (05 Mar 2000) |
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| Vieussens' annulus | A muscular ring surrounding the fossa ovalis in the wall of the right atrium of the heart. Synonym: annulus ovalis, margin of fossa ovalis, Vieussens' annulus, Vieussens' isthmus, Vieussens' limbus, Vieussens' ring. (05 Mar 2000) |
| periseptal annulus | Organelle associated with cell division in gram-negative bacteria. There are two circumferential zones of cell envelope in which membranous elements of the envelope are closely associated with murein. The annuli appear early in division and in the region between them, the periseptal compartment, the division septum is formed. (18 Nov 1997) |
| Haller's annulus | A doubling of the thoracic duct for part of its course through the thorax. Synonym: Haller's annulus. (05 Mar 2000) |