The transducer array is mounted on {HEAD ~ a carriage assembly} which moves back and forth on {TAIL ~ a pair} of rails inside a fluid compartment in the probe 
moves back on
The transducer array is mounted on { HEAD ~ a carriage assembly } which moves back and forth on { TAIL ~ a pair } of rails inside a fluid compartment in the probe
OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH REL REL OTH OTH REL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH