Femur the medial, gives attachment to the fibular collateral ligament of the knee-joint. The femur develops from the limb buds as a result of interactions between the ectoderm and the underlying mesoderm, formation occurs roughly around the fourth week of development. By the sixth week of development, the first hyaline cartilage model of the femur is formed by chondrocytes. Endochondral ossification begins by the end of the embryonic period and primary ossification centers are present in all long bones of the limbs, including the femur, by the 12th week of development. The hindlimb development lags behind forelimb development by 1–2 days.
Tibia Clausa alternate name for Doppelflöte. Most tibias are made from wood, as by Wurlitzer etc., although examples of metal tibias may be found made by the John Compton Organ Company. The Tibia Clausa, or Tibia, is generally found at 16′, 8′, 4′ and 2′ pitches as a unified rank. The mutation ranks Tibia Quint 5⅓′, Twelfth 2⅔′ and Tierce 1′ are also drawn from this unified rank of 97 pipes. In some larger organs, a second Tibia rank may be present, extended to 1′ instead of 16′, allowing a 1⅓′ Nineteenth mutation and a 1′ Piccolo to be drawn from this