84 THE ANATOMY OF THE HORSE. 



above the point of insertion. The external and internal ligaments are 

 inserted into the same tuberosity, one on each side of the attachment of 

 the middle ligament. These three ligaments may be regarded as the 

 terminal tendon of the quadriceps extensor cruris, whose action they 

 transmit to the bones of the leg. 



Synovial Membrane. This will be exposed by incising the capsular 

 ligament. It lines the inner surface of that ligament, and extends 

 upwards beyond the trochlea, forming a protrusion under the quad- 

 riceps extensor cruris. Inferiorly it is in contact with the synovial 

 membranes of the femoro-tibial joint, and sometimes it communicates 

 with them. 



It is a point worthy of notice in connection with the interior of the 

 joint, that the inner ridge of the femoral trochlea is much higher than 

 the outer; and when the patella is dislocated it is carried outwards 

 over the external ridge. 



THE FEMORO-TIBIAL ARTICULATION (FIG. 4). 



Movements. — This is a ginglymus, or hinge joint, in which the move- 

 ments are principally flexion and extension. In extension the bones of 

 the leg are carried forwards, but cannot be brought into a straight line 

 with the femur, the movement being arrested by tension of the lateral 

 ligaments and of the anterior crucial ligament. The contrary movement, 

 flexion, is finally arrested by tension of the posterior crucial ligament. 

 A slight degree of lateral movement and rotation can be produced when 

 the joint is flexed. 



Lateral Ligaments. These are two strong fibrous cords, placed one 

 on each side of the joint. The external is fixed above to the higher of 

 the two pits on the external condyle of the femur, where it covers the 

 origin of the popliteus from the lower pit. It descends over the external 

 tuberosity of the tibia, a synovial bursa being interposed, and is inserted 

 into the head of the fibula. The internal is longer, but more slender, 

 than the preceding. It is fixed above to a small tubercle on the inner 

 condyle, plays over the inner edge of the tibial articular surface, and is 

 inserted into the internal tuberosity of the tibia. 



The Posterior Ligament is of a flattened, membranous character, 

 and consists of a superficial and a deep layer, which are separable from 

 each other superiorly, but blended below. Superiorly the ligament is 

 attached to the posterior surface of the femur above the condyles ; 

 below it is inserted into the corresponding surface of the tibia, just 

 below the margin of the articular surface; while laterally its margins 

 blend with the lateral, ligaments. The superficial surface of the liga- 

 ment is related to the popliteal vessels, and to the gastrocnemius, flexor 

 perforatus, and popliteus muscles. Its deep face serves to support 



