198 



THE ARTICULATIONS OF THE HORSE 



The crucial ligaments are two strong rounded bands situated mainly in the 

 intercondyloid fossa of the femur, between the two synovial sacs. They cross 

 each other somewhat in the form of an X, and are named according to their tibial 

 attachments. The anterior crucial ligament (Ligamentum cruciatum anterius) 

 arises in the central fossa on the tibial spine, extends upward and backward, 

 and ends on the upper part of the inner surface of the external condyle of the femur. 

 The posterior crucial ligament (Ligamentum cruciatum posterius) is internal to 

 the preceding, and is somewhat larger. It is attached to an eminence at the 

 popliteal notch of the tibia, is directed upward and forward, and ends in the an- 

 terior part of the intercondyloid fossa of the femur. 



Semimembranosus 



Vastus intertnedius 



fen riitiosi^^ Branches of 



^ ' ' — - posterior fem,~ 



oral artery 

 ', Gastrocnemius 

 / {internal head) 



Popliteal 

 artery 



Patella 



Femoro- 



patellar 



joint cavity 



Middle ligament of 

 patella 



Fig. 161. — Right Stifle Joint op Horse; Sagittal Section Passing Through Outer Part of Inner Ridge 



of trochle.a. and intercondyloid fossa. 



1, Anterior crucial ligament; 2, posterior crucial ligament; 3, posterior cornu of internal semilunar cartilage; 



4, femoral ligament of external semilunar cartilage; 5, articular artery; 6, part of vastus internus. 



It may be added that these Hgaments do not He in a sagittal plane, but are somewhat twisted 

 across each other; outward rotation of the leg untwists and slackens them. 



Movements. — The principal movements of the stifle joint as a whole are 

 flexion and extension. In the ordinary standing position the articular angle 

 (behind) is about 140° to 150°. Flexion is limited only by contact of the leg with 

 the thigh if the hock is also flexed. Extension is incomplete, i. e., the femur 

 and tibia cannot be brought into the same straight line. Rotation is limited, 

 and is freest during semiflexion. The patella glides on the femoral trochlea up- 

 ward in extension, downward in flexion. 



Extension is checked mainly by tension of the crucial and lateral ligaments. In extreme 

 extension, which is accompanied by slight outward rotation of the leg, the patella can he pushed 

 upward and inward so that its fibro-cartilage hooks over the upper end of the inner ridge of the 

 trochlea, but it will not remain there imh^ss held in position. When pressure is removed, the base 

 of the patella tips forward and the cartilage lies upon the most prominent part of the trochlear 



