Each carriage has {TAIL ~ a rearwardly projecting tongue}, slidably received in {HEAD ~ a slot} formed in flange structure on the port plate 
Each carriage has { TAIL ~ a rearwardly projecting tongue } , slidably received in { HEAD ~ a slot } formed in flange structure on the port plate
OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH