The peripheral region of the ABO is made of small columns shaped like cones. They They are perpendicular to the surface.
I have colored some of them in purple in all the photomicrographs. Check them: magnify by clicking on the yellow square and do not forget to look at the TEM.

(if you wish it.)

Each column is made of three parts:
- 1: top part - most superficial: made of microvilli
- 2: intermediate part - many folds present
- 3: lower part - smooth - make most of the column.
I have labelled all the photomicrographs. Check them.

(if you wish it.)

When the spaces (= interstitial spaces) between columns are well developed (look at *), it is easy to spot the columns on a TEM photomicrograph. But when these spaces are minimal or that there are no spaces at all, it becomes harder to differentiate each individual columns.