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