| ostium appendicis vermiformis | The opening of the vermiform appendix into the lumen of the caecum. Synonym: ostium appendicis vermiformis. (05 Mar 2000) |
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| ostium arteriosum | An atrioventricular opening which leads from the left atrium into the left ventricle of the heart. Synonym: ostium atrioventriculare sinistrum, ostium arteriosum. (05 Mar 2000) |
| ostium atrioventriculare dextrum | An atrioventricular opening which leads from the right atrium into the right ventricle of the heart. Synonym: ostium atrioventriculare dextrum, ostium venosum cordis. (05 Mar 2000) |
| ostium atrioventriculare sinistrum | An atrioventricular opening which leads from the left atrium into the left ventricle of the heart. Synonym: ostium atrioventriculare sinistrum, ostium arteriosum. (05 Mar 2000) |
| ostium cardiacum | The trumpet-shaped opening of the oesophagus into the stomach. Synonym: ostium cardiacum, cardiac opening, oesophagogastric orifice. (05 Mar 2000) |
| ostium ileocaecale | The opening of the terminal ileum into the large intestine at the transition between the caecum and the ascending colon. Synonym: ostium ileocaecale, ileocaecal opening. (05 Mar 2000) |
| ostium internum | The uterine opening of the oviduct. Synonym: ostium uterinum tubae, ostium internum, uterine opening of uterine tubes. (05 Mar 2000) |
| ostium of vermiform appendix | The opening of the vermiform appendix into the lumen of the caecum. Synonym: ostium appendicis vermiformis. (05 Mar 2000) |
| ostium pharyngeum tubae auditivae | An opening in the upper part of the nasopharynx about 1.2 cm behind the posterior extremity of the inferior concha on each side. Synonym: ostium pharyngeum tubae auditivae, pharyngeal opening of eustachian tube. (05 Mar 2000) |
| ostium primum | In the embryonic heart, the temporary opening between right and left atria situated between the lower margin of the septum primum and the atrioventricular canal cushions, in an adult heart, the abnormal persistence of the so-named communication which is normal in young embryos. Synonym: foramen subseptale, ostium primum, primary interatrial foramen. (05 Mar 2000) |
| ostium pyloricum | The opening between the stomach and the superior part of the duodenum. Synonym: ostium pyloricum, gastroduodenal orifice. (05 Mar 2000) |
| ostium secundum | A secondary opening appearing in the upper part of the septum primum in the sixth week of embryonic life, just prior to the closure of the interatrial foramen primum. Synonym: ostium secundum, secondary interatrial foramen. (05 Mar 2000) |
| ostium trunci pulmonalis | The opening of the pulmonary trunk from the right ventricle, guarded by the pulmonary valve. Synonym: ostium trunci pulmonalis, pulmonary orifice. (05 Mar 2000) |
| ostium tympanicum tubae auditivae | An opening in the anterior part of the tympanic cavity below the canal for the tensor tympani muscle. Synonym: ostium tympanicum tubae auditivae, tympanic opening of eustachian tube. (05 Mar 2000) |
| ostium ureteris | The opening of the ureter in the bladder, situated one at each lateral angle of the trigone; wide gaping of the ostium usually indicates vesicoureteral reflux. Synonym: ostium ureteris, orificium ureteris, ureteral meatus, ureteral opening. (05 Mar 2000) |