whereby, {HEAD ~ a transmitter} and a receiver received in said recess means can be pressed against {TAIL ~ diametrically opposite surface areas} of a body protruding part 
pressed against
whereby , { HEAD ~ a transmitter } and a receiver received in said recess means can be pressed against { TAIL ~ diametrically opposite surface areas } of a body protruding part
OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH REL REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH