An activation button exposed through the top of {HEAD ~ the assembly} is depressed to actuate a switch assembly which, in turn, actuates {TAIL ~ a drive mechanism} 
An activation button exposed through the top of { HEAD ~ the assembly } is depressed to actuate a switch assembly which , in turn , actuates { TAIL ~ a drive mechanism }
OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL