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a slight constriction of the aorta immediately distal to the left subclavian artery at the point of attachment of the ductus arteriosus.
A constriction in the fetal aorta between the ductus arteriosus and the left subclavian artery. The condition sometimes persists into adulthood.
See also: isthmus
a narrow connection between two larger bodies or parts.
that part of the aorta between the origin of the brachiocephalic trunk, or the left subclavian artery, and that of the ductus arteriosus which is partly constricted in the fetus; it marks the partial separation of fetal blood flow derived from right and left ventricles, and is most conspicuous in the newborn calf.
isthmus of auditory tube
the narrowest part of the pharyngotympanic tube at the junction of its bony and cartilaginous parts. Called also isthmus of pharyngotympanic tube.
isthmus of fauces, isthmus faucium
the constricted aperture between the cavity of the mouth and the pharynx.
the short slightly narrower section of the oviduct of the bird between the magnum and the uterus, where the shell membranes are laid down.
the aperture between the dorsal and ventral parts of the pharynx and separated by the free edge of the soft palate and the palatopharyngeal arch.
isthmus of pharyngotympanic tube
see isthmus of auditory tube (above).
isthmus of rhombencephalon
the narrow segment of the fetal brain, forming the plane of separation between the rhombencephalon and cerebrum.
isthmus of thyroid
the band of tissue joining the lobes of the thyroid. It is fibrous in sheep and horses and glandular in dogs and cattle.
isthmus of uterine tube
the narrower, thicker-walled portion of the uterine tube closest to the uterus.