The first and second channels {HEAD ~ each} have {TAIL ~ a flange} extending from one wall to adjacent opposed wall to define the elongated opening into the channel 
have
The first and second channels { HEAD ~ each } have { TAIL ~ a flange } extending from one wall to adjacent opposed wall to define the elongated opening into the channel
OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH