isthmus, pl. isthmi isthmuses (is´mus, -mI, -mus-ez)

1. A constriction connecting two larger parts of an organ or other anatomical structure. 2. A narrow passage connecting two larger cavities. 3. The narrowest portion of the brainstem at the junction between midbrain and hindbrain. [G. isthmos]
i. of aorta a slight constriction of the aorta immediately distal to the left subclavian artery at the point of attachment of the ductus arteriosus.i. aortae [NA] ;
i. aor´tae [NA] i. of aorta
i. of auditory tube the narrowest portion of the auditory tube at the junction of the cartilaginous and bony portions.i. tubae auditivae [NA], i. of eustachian tube;
i. of cartilage of ear a narrow bridge connecting the cartilage of the external acoustic meatus and the lamina of the tragus with the main portion of the cartilage of the auricle.i. cartilaginis auris [NA] ;
i. cartilag´inis au´ris [NA] i. of cartilage of ear
i. of cingulate gyrus 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.i. gyri cinguli [NA], i. of gyrus fornicatus, i. of limbic lobe;
i. of eustachian tube i. of auditory tube
i. of external acoustic meatus the narrowest portion of this canal in the bony part near its deep termination.i. meatus acustici externi;
i. 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.i. faucium [NA] ;
i. fau´cium [NA] i. of fauces
i. glan´dulae thyroid´eae [NA] i. of thyroid
Guyon's i. i. of uterus
i. gy´ri cin´guli [NA] i. of cingulate gyrus
i. of gy´rus fornica´tus i. of cingulate gyrus
i. of His rhombencephalic i
Krönig's i. the narrow straplike portion of the resonant field that extends over the shoulder, connecting the larger areas of resonance over the pulmonary apex in front and behind.
i. of limbic lobe i. of cingulate gyrus
i. mea´tus acus´tici exter´ni i. of external acoustic meatus
pharyngeal i. communicating space between nasopharynx and oropharynx, sealed off by elevation of the soft palate and contraction of portions of the superior pharyngeal constrictor (palatopharyngal sphincter) during swallowing.
i. pharyngonasa´lis choana
i. pros´tatae [NA] i. of prostate
i. of prostate the narrow middle part of the prostate anterior to the urethra.i. prostatae [NA] ;
i. rhombenceph´ali [NA] rhombencephalic i
rhombencephalic i. 1. a constriction in the embryonic neural tube delineating the mesencephalon from the rhombencephalon; 2. the anterior portion of the rhombencephalon connecting with the mesencephalon.i. rhombencephali [NA], i. of His;
i. of thyroid the central part of the thyroid gland joining the two lateral lobes.i. glandulae thyroideae [NA] ;
i. tu´bae auditi´vae [NA] i. of auditory tube
i. tu´bae uteri´nae [NA] i. of uterine tube
i. u´teri [NA] i. of uterus
i. of uterine tube the narrow portion of the uterine tube adjoining the uterus.i. tubae uterinae [NA] ;
i. of uterus an elongated constriction at the junction of the body and cervix of the uterus.i. uteri [NA], Guyon's i., orificium internum uteri, os uteri internum, ostium uteri internum;
Vieussens' i. limbus fossae ovalis


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