{HEAD ~ a passage} positioned at {TAIL ~ the second end} of the housing and traversing from the top surface to the bottom surface 
positioned at
{ HEAD ~ a passage } positioned at { TAIL ~ the second end } of the housing and traversing from the top surface to the bottom surface
HEAD HEAD HEAD HEAD HEAD HEAD REL REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH