(n.) The Eustachian tube, or the Fallopian tube.

Eustachian tube Fallopian tube aqueduct arroyo bed bottleneck canalization canalize carve chamfer channel chisel conduit corrugate course crack creek bed crimp culvert cut dado defile dike ditch donga dry bed duct emunctory engrave entrenchment fistula flume flute fosse furrow gash goffer gouge groove gulch gully gullyhole gutter ha-ha headrace incise intestines irrigation ditch isthmus kennel meatus moat narrow narrows neck nullah ostium oviduct pass pleat plow pore rabbet race rifle river bed riverway runnel rut salpinx score scratch slit sluice spillbox spillway strait streak stream bed streamway striate sunk fence swash swash channel tailrace thoracic duct throat trench trough ureter urethra vagina vas vessel wadi water carrier water channel water furrow water gap water gate watercourse waterway waterworks wrinkle