Collectors or {HEAD ~ drains} of {TAIL ~ the first and fourth transistors} are coupled together and collectors or drains of the second and third transistors are coupled together 
of
Collectors or { HEAD ~ drains } of { TAIL ~ the first and fourth transistors } are coupled together and collectors or drains of the second and third transistors are coupled together
OTH OTH HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH