=Ligaments.=—The =lateral femoro-patellar ligaments=, external and internal (Ligamentum femoro-patellare fibulare, tibiale), are two thin bands which reinforce the capsule on either side. The external ligament is fairly distinct; it arises from the external epicondyle of the femur just above the lateral femoro-tibial ligament, and ends on the external border of the patella. The internal ligament is thinner and is not distinct from the capsule; it arises above the internal epicondyle, and ends on the patellar fibro-cartilage. The =patellar ligaments= (Ligamenta patellæ), also called the straight ligaments of the patella, are three very strong bands which attach the patella to the tuberosity of the tibia. The =external patellar ligament= is attached above to the outer part of the anterior surface of the patella, and below to the outer part of the tuberosity. It receives a strong tendon from the biceps femoris muscle. The =middle patellar ligament= extends from the front of the apex of the patella to the lower part of the groove on the tuberosity of the tibia, a bursa being interposed between the ligament and the upper part of the groove. The =internal patellar ligament= is attached above to the patellar fibro-cartilage, and ends on the tuberosity of the tibia, internally to the groove. It is joined by the common aponeurosis of the gracilis and sartorius. These so-called ligaments are, in reality, the tendons of insertion of the quadriceps femoris muscle, and transmit the action of the latter to the tibia; they also function similarly for the other muscles attached to them as noted above. It will be noticed that the upper attachments are further apart than the lower ones, so that the ligaments converge below. The inner ligament is especially oblique. The middle ligament is more deeply placed than the others, and therefore cannot usually be felt distinctly in the living animal. [Illustration: FIG. 158.—SEMILUNAR CARTILAGES AND CRUCIAL LIGAMENTS OF RIGHT STIFLE OF HORSE. _F_, Femoral ligament of external cartilage. (After Schmaltz, Atlas d. Anat. d. Pferdes.) ] The =femoro-tibial articulation= (Articulatio femoro-tibialis) is formed between the condyles of the femur, the proximal end of the tibia, and the interposed semilunar cartilages. =Articular Surfaces.=—The condyles of the femur are slightly oblique in direction. The articular surface of the outer one is more strongly curved than that of the inner one; the latter is confluent below with the inner ridge of the trochlea, while the narrow ridge which connects the external condyle with the trochlea is usually non-articular. The saddle-shaped surfaces of the condyles of the tibia are not adapted to the femoral condyles, and are in contact with only a small part of them. [Illustration: FIG. 159.—PROXIMAL ENDS OF RIGHT TIBIA AND FIBULA OF HORSE, WITH SEMILUNAR CARTILAGES AND CRUCIAL LIGAMENTS, EXTERNAL VIEW. (After Schmaltz, Atlas d. Anat. d. Pferdes.) ]