NB: Convention: Tube begins on intervallum side.
Zone A: Intervallum side.
Canal: Pore modified by skeletal structure thikening or by lintels streching. Canal length is greater than perforation diameter.
Lintel: Skeletal structure separating and bounding adjacent pores/canals.
Carcass: Part of wall on intervallum side.
IW: Inner wall.
Downwardly opening: Opening on intervallum side is higher than the other one.
Upwardly opening: Opening on intervallum side is lower down than the other one.
Type of carcass perforations: inner wall (IW) | |_ Direction of carcass canals tubes zone A (IW)