adaxial

On the side that is towards the axis or central line, usually on the upper side.

[…]it has been transformed, except in a few taxa where lobules are always explanate, into a galeate water-sac, which is formed wholly from the lobule, with the external surface from the adaxial leaf surface.

adjacent to the axis, or in vertebrates the notochord.

In zebrafish, the adaxial cells are precursors to the embryonic slow muscle fibers.