| 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) |
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| 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 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) |
| ostium urethrae externum | The slitlike opening of the urethra in the glans penis, the external orifice of the urethra (in the female) in the vestibule, usually upon a slight elevation, the papilla urethrae. Synonym: ostium urethrae externum, external opening of urethra, meatus urinarius, orificium urethrae externum. (05 Mar 2000) |
| ostium urethrae internum | The internal opening or orifice of the urethra, at the anterior and inferior angle of the trigone. Synonym: ostium urethrae internum, internal urethral opening. (05 Mar 2000) |
| ostium uteri | The vaginal opening of the uterus. Synonym: ostium uteri, mouth of the womb, opening of uterus, orificium externum uteri, os uteri externum, ostium uteri externum. (05 Mar 2000) |
| ostium uteri externum | The vaginal opening of the uterus. Synonym: ostium uteri, mouth of the womb, opening of uterus, orificium externum uteri, os uteri externum, ostium uteri externum. (05 Mar 2000) |
| ostium uteri internum | An elongated constriction at the junction of the body and cervix of the uterus. Synonym: isthmus uteri, Guyon's isthmus, orificium internum uteri, os uteri internum, ostium uteri internum. (05 Mar 2000) |
| ostium uterinum tubae | The uterine opening of the oviduct. Synonym: ostium uterinum tubae, ostium internum, uterine opening of uterine tubes. (05 Mar 2000) |
| ostium vaginae | The narrowest portion of the canal, in the floor of the vestibule posterior to the urethral orifice. Synonym: ostium vaginae, orificium vaginae, vaginal opening. (05 Mar 2000) |
| ostium venae cavae inferioris | The orifice through which the inferior vena cava opens into the right atrium. Synonym: ostium venae cavae inferioris, orifice of inferior vena cava. (05 Mar 2000) |
| ostium venae cavae superioris | The point of entry of the superior vena cava into the right atrium. Synonym: ostium venae cavae superioris, orifice of superior vena cava. (05 Mar 2000) |