86 THE ANATOMY OF THE HORSE. 



one covers, in addition, the tendon of origin of the popliteus, and the 

 common tendon of origin of the flexor metatarsi and extensor of the 

 digit. 



Directions. — The posterior ligament should now be cut away ; and, 

 the patella being thrown down, the synovial membrane and fat should 

 be removed from the front of the joint. The joint should then be 

 strongly flexed, in order to expose, as far as possible, the crucial liga- 

 ments in the intercondyloid groove. The rims of the semilunar 

 cartilages and their coronary ligaments will at the same time be 

 exposed. 



The Crucial Ligaments are two strong fibrous cords stretching be- 

 tween the femur and the tibia, and lodged in the intercondyloid groove. 

 They cross one another somewhat like the limbs of the letter X, and 

 hence their name. They are distiuguised as anterior and posterior. The 

 anterior, the most external of the two, is attached superiorly to the 

 intercondyloid groove, and to the external condyle of the femur where 

 it bounds that groove. Its fibres have a slightly spiral arrangement, 

 and extend downwards and forwards to be inserted into the outer aspect 

 of the tibial spine. The posterior ligament is longer than the anterior, 

 and is fixed superiorly to the intercondyloid groove and inner condyle. 

 It extends downwards and backwards to be fixed to a special tubercle 

 on the back of the tibia below the rim of its articular surface. These 

 two ligaments bind the femoral and tibial articular surfaces closely 

 together, and at the same time restrict the movements of the joint, the 

 anterior ligament being put upon the stretch during extension, and 

 finally arresting that movement, while the posterior ligament plays the 

 same part with regard to flexion. 



The Inter-articular or Semilunar Fibro-cartilagbs. These are two 

 crescentic or sickle-shaped pieces of fibro-cartilage, interposed between 

 the condyles of the femur and the articular surface of the tibia. The 

 convex margin of each is turned outwards, and is much thicker than the 

 concave edge, which embraces the tibial spine, and is so thin as to be 

 translucent. The lower surface of each is flattened to rest on the tibia, 

 but the upper surface is hollowed to embrace the femoral condyle. 

 They are fixed in position as follows : — The anterior extremity of the 

 inner fibro-cartilage is fixed into an excavation in front of the tibial 

 spine, while its posterior end is similarly fixed behind the spine. The 

 outer cartilage is fixed by its anterior extremity in front of the spine, 

 while its posterior extremity is bifid, having an upper slip inserted into 

 a depression at the posterior part of the intercondyloid groove, and a 

 lower into the rim of the tibial articular surface, partly under cover of 

 the posterior interosseous ligament. These slips of insertion at the 

 extremities of the fibro-cartilages are sometimes termed the coronary 

 ligaments, three of which belong to the outer, and two to the inner. 



