Answer
Up to early in the 7th week of embryonic development, the upper and lower limb buds can be seen to have similar orientation with respect to the body. The future lower limbs are like small paddles sticking out from the body with the soles facing each other. Also, the future paddlelike upper limbs stick out with palms facing each other. During the seventh week of gestation, reorientations of the limbuds take place: the upper limbs rotate laterally, and the pollexes turn out.
Work Step by Step
Unlike the upper limbs, the lower limb buds rotate medially, so the soles of the feet turn down and each hallux assumes a medial position.
This reorientation of the limb buds during the seventh week of embryonic development, changes the position of the flexor muscles of the elbow and the knee : the biceps brachii, and brachialis assume positions in the anterior compartment of the upper arm and flex the forearm forwards and upwards from a zero position. In contrast, the hamstring muscles, now in the posterior compartment of the thigh, flex the leg at the knee joint upwards, but backwards from zero position.
