Final answer:
The femur is the most proximal bone in the thigh, being the longest and strongest bone in the body and playing a crucial role in supporting weight and enabling leg mobility.
Step-by-step explanation:
The most proximal part of the lower extremity in the thigh is the femur, which is found between the hip joint and knee joint. The femur is the single bone of the thigh and is the longest and strongest bone in the body. It accounts for about one-quarter of a person's total height. The proximal end, the head of the femur, articulates with the acetabulum of the hip bone to form the hip joint. This robust bone supports the body's weight and enables mobility of the lower limb.