- 1. A constriction in the embryonic neural tube delineating the anterior portion of the rhombencephalon, the future metencephalon, form the more rostrally located mesenephalon. 2. SYN: rhombencephalic i.. [G. isthmos]- i. aortae [TA] SYN: aortic i..- aortic i. [TA] a slight constriction of the aorta immediately distal to the left subclavian artery at the point of attachment of the ductus arteriosus. SYN: i. aortae [TA], i. of aorta.- i. of cartilaginous auricle [TA] 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. SYN: i. cartilaginis auris, i. of cartilage of ear.- i. cartilaginis auricularis [TA]- i. of cingulate gyrus [TA] 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. SYN: i. gyri cinguli [TA], i. of gyrus fornicatus, i. of limbic lobe.- i. of external acoustic meatus the narrowest portion of this canal in the bony part near its deep termination. SYN: i. meatus acustici externi.- i. of fauces [TA] 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. SYN: i. faucium [TA], oropharyngeal i..- i. of His SYN: rhombencephalic i..- Krönig 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. pharyngonasalis SYN: choanae.- i. of pharyngotympanic tube [TA] the narrowest portion of the auditory tube at the junction of the cartilaginous and bony portions. SYN: i. tubae auditivae [TA], i. tubae auditoriae, i. of auditory tube, i. of eustachian tube.- i. of pharynx [TA] passage posterior to the soft palate by which the nasopharynx and oropharynx communicate (i.e., the junction of naso- and oropharynx), closed during swallowing by elevation of the soft palate and contraction of the posterior fascicle of palatopharyngeus (muscle), forming a Passavant cushion. SYN: i. pharyngis, pharyngeal i..- i. of prostate [TA] the narrow middle part of the prostate anterior to the urethra. SYN: i. prostatae [TA].- i. rhombencephali SYN: 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. SYN: i. (2) [TA], i. of His, i. rhombencephali.- i. of thyroid gland [TA] the central part of the thyroid gland joining the two lateral lobes. SYN: i. glandulae thyroideae [TA].- i. tubae auditoriae i. of pharyngotympanic tube.- i. of uterine tube [TA] the narrow portion of the uterine tube adjoining the uterus. SYN: i. tubae uterinae [TA].- i. of uterus [TA] an elongated constriction at the junction of the body and cervix of the uterus. SYN: i. uteri [TA], Guyon i., orificium internum uteri, os uteri internum, ostium uteri internum.- Vieussens i. SYN: limbus fossae ovalis.
* * *isth·mus 'is-məs n a contracted anatomical part or passage connecting two larger structures or cavities: asa) an embryonic constriction separating the midbrain from the hindbrainb) the lower portion of the uterine corpus
* * *n.a constricted or narrowed part of an organ or tissue, such as the band of thyroid tissue connecting the two lobes of the thyroid gland.
* * *isth·mus (isґməs) pl. isthґmi [L., from Gr. isthmos] a narrow connection between two larger bodies or parts. isthmian, isthmic adj
Medical dictionary. 2011.