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Lower Limb Embryology

eMedicine Surgery, 2014

Development Historically, descriptions of lower limb development and embryology have relied solely on detailed descriptions of the gross morphology of the developing embryo.
Morphologic description is thus the foundation upon which our understanding of the complex and highly regulated process of limb outgrowth is based.
An overview of this gross morphologic schema provides a framework for further studying the processes of regulation and patterning involved in the development of the lower extremity.
The first visible hint of the developing lower extremity is a swelling located on the ventrolateral surface of the 3-week-old embryo.
A true limb bud then develops during the fourth postovulatory week (3-6 mm crown-to-rump length), a few days after the appearance of the upper limb bud.
Over the next few days, the bud develops a distinctive morphology with a flattened ventral surface and a rounded dorsum.
This transient structure (which lingers a week to the 16-20 mm stage) is critical to maintaining limb outgrowth.
As the fourth week ends, 3 regions have developed corresponding to the thigh, leg, and foot (8-11 mm stage).
Morphologically, the foot is divided into two craniad (preaxial) and caudad (postaxial) regions linked with the tibia and fibula.
In the 14 mm embryo, the foot will continue to develop so that the 5 rays evolve into a more fanlike structure.
The tibial surface is cephalad and the extensor surface of the foot faces laterally while the plantar or flexor surface of the foot faces medially.