| isthmus of eustachian tube | The narrowest portion of the auditory tube at the junction of the cartilaginous and bony portions. Synonym: isthmus tubae auditivae, isthmus of eustachian tube. (05 Mar 2000) |
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| isthmus of external acoustic meatus | The narrowest portion of this canal in the bony part near its deep termination. Synonym: isthmus meatus acustici externi. (05 Mar 2000) |
| isthmus of fauces | The constricted and short space which establishes the connection between the cavity of the mouth and the oro-pharynx, bounded anteriorly by the palatoglossal folds and posteriorly by the palatopharyngeal folds; the lateral well is the tonsillar fossa. Synonym: isthmus faucium. (05 Mar 2000) |
| isthmus of gyrus fornicatus | The narrowing of the cingulate gyrus, at its transition with the hippocampal gyrus behind and below the splenium of the corpus callosum, caused by the anterior extension of the conjoined parieto-occipital and calcarine sulci. Synonym: isthmus gyri cinguli, isthmus of gyrus fornicatus, isthmus of limbic lobe. (05 Mar 2000) |
| isthmus of His | A constriction in the embryonic neural tube delineating the mesencephalon from the rhombencephalon, the anterior portion of the rhombencephalon connecting with the mesencephalon. Synonym: isthmus rhombencephali, isthmus of His. (05 Mar 2000) |
| isthmus of limbic lobe | The narrowing of the cingulate gyrus, at its transition with the hippocampal gyrus behind and below the splenium of the corpus callosum, caused by the anterior extension of the conjoined parieto-occipital and calcarine sulci. Synonym: isthmus gyri cinguli, isthmus of gyrus fornicatus, isthmus of limbic lobe. (05 Mar 2000) |
| isthmus of prostate | The narrow middle part of the prostate anterior to the urethra. Synonym: isthmus prostatae. (05 Mar 2000) |
| isthmus of thyroid | The central part of the thyroid gland joining the two lateral lobes. Synonym: isthmus glandulae thyroideae. (05 Mar 2000) |
| isthmus of uterine tube | The narrow portion of the uterine tube adjoining the uterus. Synonym: isthmus tubae uterinae. (05 Mar 2000) |
| isthmus of uterus | 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) |
| isthmus pharyngonasalis | The opening into the nasopharynx of the nasal cavity on either side. Synonym: isthmus pharyngonasalis, posterior naris, postnaris. Origin: Mod. L. Fr. G. Choane, a funnel (05 Mar 2000) |
| isthmus prostatae | The narrow middle part of the prostate anterior to the urethra. Synonym: isthmus prostatae. (05 Mar 2000) |
| isthmus rhombencephali | A constriction in the embryonic neural tube delineating the mesencephalon from the rhombencephalon, the anterior portion of the rhombencephalon connecting with the mesencephalon. Synonym: isthmus rhombencephali, isthmus of His. (05 Mar 2000) |
| isthmus tubae auditivae | The narrowest portion of the auditory tube at the junction of the cartilaginous and bony portions. Synonym: isthmus tubae auditivae, isthmus of eustachian tube. (05 Mar 2000) |
| isthmus tubae uterinae | The narrow portion of the uterine tube adjoining the uterus. Synonym: isthmus tubae uterinae. (05 Mar 2000) |