Development of the Musculoskeletal System: Bones of the limbs

The upper limb buds form one week before the legs. The Upper limb bud forms @ the level of the pericardial swelling, below the diaphragm. The hind limb bud forms @ the umbilical cord. The lateral plate mesenchyme form the bones, ligaments, tendons and vessels. The buds begin as cones, then become flippers, and then progress to the appendages that we know today. The elbows and knees are bent ventrally to start, so that the palms and soles are facing the midline.
Limb rotation:
Upper: 90 degrees external rotation Lower: 90 degrees internal rotation It is not until you are two that the arms are shorter than the legs.Aging the fetus by bones: 6-8 mos. – calcaneous and talus are calcified
Full term: secondary ossification centers in the distal femur and the upper end of the tibia, also the cuboid is formed.

Category: Anatomy Notes