The<unk>  is the region at the interface between the non-lymphoid red pulp and the lymphoid white-pulp of the spleen. (Some sources consider it to be the part of red pulp which borders on the white pulp, while other sources consider it to be neither red pulp nor white pulp.) A<unk>  also exists in lymph nodes.
Marginal zone
Blue zone
Inner nuclear layer
Watershed area 
Outer nuclear layer
Trigger zone
Episcleral layer
Sommer's sector