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