an elastic membrane covering an opening arrangement formed in {HEAD ~ a wall} of said passage to communicate a first side of {TAIL ~ said membrane} with pressure in said passage 
an elastic membrane covering an opening arrangement formed in { HEAD ~ a wall } of said passage to communicate a first side of { TAIL ~ said membrane } with pressure in said passage
OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH