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