418 THE AXATOMY OF THE HORSE 



THE PASTERN JOINT 



The several jiarts which enter into the formation of this joint are the two 

 lateral condyles on the inferior extremity of the os suffraginis, and the 

 corresponding cavities on the os coronse. This last surface is completed 

 behind by a very dense and thick fibro-cartilage, which acts partl}^ as a 

 ligament, and partly by increasing the depth of the articular surface. It is 

 attached above by six fibi'ous bands, of which two are continuous with the 

 inferior sesamoideal ligaments, and four pass on to the sides of the os 

 suiFraginis. Below it is fixed to the os coronse, between the articular surface 

 and the tubercle behind it. This fibro-cartilage forms a smooth sui-face 

 posteriori}- for the flexor pedis perforans to play over, and is continuous on 



Fig. 52. — External View of the Pastern 

 Joint. 



A. Inferior third of the large metacarpal 

 bone. 



B. External sesamoid bone. 



C. Suffragineal bone. 

 n. Coronal bone. 



E. Navicular bone. 



F. Pedal bone. 



1. One division of the suspensory liga- 

 ment. 



2. Lateral sesamoideal ligament (external). 



3. Ligamentous fibres given to the exten- 

 sor pedis tendon by the suspensory 

 ligament. 



4. Inferior superficial sesamoideal liga- 

 ment. 



5. C. 7. Extensor pedis tendon. 



8. External lateral ijhalangio - pedal liga- 

 ment. 



9. External lateral cartilage. 



each side with the two divisions of the flexor perforatus. In addition to 

 these structures, and the synovial capsules lining them, the joint is pro- 

 tected by two lateral ligaments, and in front by the extensor tendon. 



The lateral ligaments, thick and strong, take an oblique direction from 

 above downwards, and from before backwards, one on each side of the joint. 

 They arise from two depressions, just below the tubercles on the lateral 

 parts of the os suffraginis, and terminate at the superior edge of the os 

 coronse. Their lowest fibres prolong themselves beyond this bone to gain 

 the extremities of the os naviculare, and constitute the posterior lateral 

 ligaments of the cofiin joint. 



The synovial membrane lines the posterior surface of the extensor tendons 

 anteriorl}', the lateral ligaments, and the fibro-cartilage ; it forms posteriorly 

 a cul de sac, which mounts up between this and the posterior surface of the 

 OS suffragin's. 



The M0VE.MENTS of this joint are simply of extension and flexion when 

 the muscles are in action ; but when they are relaxed there is some .slight 

 lateral motion. 



