The piston head is fitted into a cylinder which divides {HEAD ~ the cylinder} into {TAIL ~ two hydraulic or pneumatic cells} 
into
The piston head is fitted into a cylinder which divides { HEAD ~ the cylinder } into { TAIL ~ two hydraulic or pneumatic cells }
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL