Changes

**This produces small buds, which will continue to grow to eventually form the limbs.

**This produces small buds, which will continue to grow to eventually form the limbs.

*Proliferation of the lateral plate mesoderm cannot sustain entire limb growth; instead the '''apical ectodermal ridge (AER)''' maintains growth.

*Proliferation of the lateral plate mesoderm cannot sustain entire limb growth; instead the '''apical ectodermal ridge (AER)''' maintains growth.

**The AER develops as mesenchymal cells cause cells of the overlying ectoderm to change their morphology from cuboidal to columnar.

**The AER develops as mesenchymal cells in the distal limb ectoderm that has locally thickened by changing their morphology from cuboidal to columnar.

**It divides the limb into dorsal and ventral halves.

**It divides the limb into dorsal and ventral halves.

**The ridge can be seen when looking at the limb bud in a distal to poximal direction.

**The ridge can be seen when looking at the limb bud in a distal to poximal direction.