418 



Till': ANATOMY oF TIIK lIOTtSE 



THE PASTERN JOINT 



The 9fveraJ {Htrts wliic-li enter iatu the fonnation uf this joint are the twd 

 lateral eunilyles on the inferior extremity of the os sullraginis, and the 

 corresi)onding cavities on the os corona;. This last surface is completed 

 l)ehind by a very dense and thick libro-cartilage, which acts partly as a 

 li','anient, and partly by increasing the depth of tlie articular surface. It is 

 attaehed above by six fibrous bands, of which two are continuous with the 

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

 suflVaginis. l.elow it is lixed to the os corona?, between the articular surface 

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

 IMjsteriorly for the flexor pedis pei-forans to play over, and is continuous on 



ii€ 



02. — External ViBW of the I'asteun 

 Joint. 



Inferior thiixl of the large metacari«>l 

 bone. 



Kxtemal scs-mioid bone. 



iSuffragineal bono. 



Coronal bone. 



Navicular bone. 



I'edal bone. 



One division of the suspensory liga- 

 ment. 



Lateral sesaraoideal ligament (external). 



Ligamentous fibres given to the exten- 

 sor )iedi3 tendon by the susiiensory 

 ligament. 



Inferior suiierficial sesamoideal liga- 

 ment. 



C. 7. Kxtensor pedis tendon. 



External lateral pUalangio - iiedal liga- 

 ment. 



External lateral cartilage. 



each side with the two divisions of the llexor pcrforatus. In addition to 

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

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



The lateral ligaments, t\nQ^ 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 

 eorona'. Their lowest fibres prolong themselves beyond this bone to gain 

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

 ligaments of the euHin joint. 



The synovial membrane lines the posterior surface of the extensor tendons 

 anteriorly, the lateral ligaments, and the fibro-cartilage ; it forms posteriori}' 

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

 OS suffraginis. 



TuE MOVEMENTS 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. 



