(is'mŭs )

[Gr. isthmos, neck (of land ), isthmus]

1. A narrow passage connecting two cavities.
2. A narrow structure connecting two larger parts.
3. A constriction between two larger parts of an organ or structure.

aortic i.A constriction in the fetal aorta between the ductus arteriosus and the left subclavian artery.

cavotricuspid i.The electrically conductive tissue that separates the inferior vena cava from the tricuspid valve. It is the part of the atrium in which the reentrant electrical activity of atrial flutter circulates.

i. of eustachian tube The narrowest section of the auditory tube, where the bony canal meets the cartilaginous tube.

i. of the fauces A constriction connecting the oral cavity proper with the pharynx. The walls of the isthmus are the palatoglossal arches.

pharyngeal i.The passageway between the nasopharynx and oropharynx.

i. of thyroid gland A narrow band of thyroid tissue connecting the right and left lobes of the thyroid gland .

i. uteri Isthmus of uterus.

i. of uterine tube The thick-walled segment of the uterine (fallopian) tube just before it enters the wall of the uterus.

i. of uterus A narrowing of the body of the uterus just above the cervix.

isthmic, adj.