Knee. Three bones enter into the formation of the knee-joint - the femur, the tibia, and the patella or knee-cap. This last-named bone is an example of what is known as a, sesamoid bone, being an ossified portion of the tendon of the great extensor-muscle, which lies in front of the thigh. The connection of the lower part of the patella with the tibia is called the ligamentum patella'. This ligament is really the extremity of the tendon of the afore-mentioned muscle; the patella being interposed between the ligament and the muscle proper. The knee-joint is one of the largest and most important in the body. It possesses a capsular ligament and numerous other ligaments, the most important of which are what are known as the crucial ligaments, two strong bands connecting the femur and tibia, and disposed crosswise. For the diseases to which it is subject see Joints, Diseases of. The patella, from its exposed situation, is liable to injury; fracture of the patella not infrequently occurs, however, apart from external violence, as the result of muscular action, in cases where a person who is about to fall makes a violent attempt to recover his equilibrium.