This is the corresponding joint to the knee of man. It is formed by the union of the femur with the tibia on the one part, and with the patella or knee-cap on the other. The femur articulates with the upper extremity of the tibia by its two condyles, and with the patella by its two ridges or trochlea in front. Between the two condyles and the head of the tibia there are two crescentic pieces of fibro-cartilage (semilunar cartilages) which serve to mould the rounded condyles of the thigh-bone upon the flatter articular face of the tibia.

The three bones composing this joint are united by numerous strong ligaments, so disposed as to permit the greatest freedom of motion, while at the same time offering adequate resistance to the great strain which is thrown upon them.

The ligaments are divisible into three sets, viz. those which connect the patella to the femur and tibia; those which unite the two last-named bones together; and those which attach the semilunar cartilages to them.