serial sections in the transverse body plane were used to determine the volume of the limb bud and of its parts -- namely , the apical ectodermal ridge , the ectodermal epithelium , the coat zone , the vascular zone , and the plug during the period between the onset of its formation ( hamburger and hamilton 's stage 17 ) and the stage of nerve fibre ingrowth ( hh 22 + ) .
C0282505
limb bud
C1516037
apical ectodermal ridge