Anatomy

Sociology

Limb bud

Ectoderm

Population

Mathematics

Evolutionary biology

Zone of polarizing activity

Limb development

Biology

Gene

Demography

Vertebrate

Embryogenesis

Numerical digit

Morphogenesis

Genetics

Arithmetic

Development

ABSTRACT The vertebrate limb continues to serve as an influential model of growth, morphogenesis and pattern formation. With this Review, we aim to give an up-to-date picture of how a population of undifferentiated cells develops into the complex pattern of the limb. Focussing largely on mouse and chick studies, we concentrate on the positioning of the limbs, the formation of the limb bud, the establishment of the principal limb axes, the specification of pattern, the integration of pattern formation with growth and the determination of digit number. We also discuss the important, but little understood, topic of how gene expression is interpreted into morphology.

Establishing the pattern of the vertebrate limb