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