A lower arm has {HEAD ~ one end} connected to the base rotatable joint member and another end connected to {TAIL ~ a central joint member} 
A lower arm has { HEAD ~ one end } connected to the base rotatable joint member and another end connected to { TAIL ~ a central joint member }
OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL