Skeletal pattern and joints formation were examined in chick limb bud grafts using the chorioallantoic grafting method which enabled the separation of the limb bud from the body wall and also restricted the influence of some of the morphogenetic zones of the limb. The embryonic chick limb buds from the experimental group were transplanted without the prospective anterior necrotic zone (ANZ) or the posterior necrotic zone (PNZ). Transplants with intact limb bud material served as the control group. Elimination of the ANZ or PNZ mainly affected the skeleton of the zeugopod and elbow joint. Most grafts lacking the ANZ or PNZ showed fusion of the ulna and radius and complete regression of the elbow joint. The most common abnormality was fusion of the humerus, ulna and radius into a single cartilaginous block which was rarely observed in control grafts. As the separation of the ulna and radius depends on cell death in the "opaque patch', it is likely that mechanical elimination of the ANZ or PNZ suppressed cell death in this zone and caused a typical fusion in the zeugopod skeleton and elbow joint and growth retardation in grafts lacking the ANZ or PNZ.
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