it has been suggested that one of the major functions of the apical ectodermal ridge ( aer ) of the embryonic chick limb-bud is to maintain mesenchymal cells directly subjacent to it ( i.e . cells extending 0.4 -- 0.5 mm from the aer ) in a labile , undifferentiated condition .
C0282505
limb-bud
C1516037
aer