Observations on the sequence of blastemal condensations in the limbs of the mouse embryo

Abstract

Abstract In the forelimbs, the sequence of blastemal condensation is: scapula and humerus, ulna, digit IV, digit V, radius, digit III, digit II, digit I. In the hind limb, the sequence is: innominate bone and femur, fibula, digit IV, digit V, tibia, digit III, digit II, digit I. The sequence described may lead to loss of preaxial parts of the limb in cases of severe over‐all reduction of limb bud material due to genetic or teratogenic agents. The main reason why ectrodactyly and polydactyly in the mouse are usually preaxial is the localization for some unknown reason of alterations in growth rate in the preaxial margin of the footplate. However, the fact that blastemal condensations begin postaxially will tend to confine these and similar skeletal anomalies of the limb to the preaxial part.