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