Each of {HEAD ~ the components}, including the mirrors, anode, and {TAIL ~ cathode}, must be sealed to the block to form a gas tight seal 
including
Each of { HEAD ~ the components } , including the mirrors , anode , and { TAIL ~ cathode } , must be sealed to the block to form a gas tight seal
OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD OTH REL OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH