38 LIGAMENTOUS STRUCTURES OF THE FOOT. 



covered by strands of tissue that act as a check ligament to the 

 flexor pedis perforans, with which they are usually so inti- 

 mately united that they might be regarded as belonging to that 

 ligament. 



As already indicated, these ligaments at their insertion into 

 the posterior part of the coronet bone combine intimately with 

 the central limb of the inferior sesamoidean ligament and with 

 the terminal portions of the flexor pedis perforatus, so as to 

 form a single mass and to pernait only of artificial separation. 



3. The Pedal or Coffin Joint 



Is formed by the union of the articular surfaces of three bones. 

 The convexity is formed by the lower articular surface of the 

 coronet bone, the concavity by the upper surface of the os pedis 

 and by the navicular bone. 



{a) All three bones are united by a synovial membrane 

 (fig. 10, g), which, as in other joints, surrounds the articular 

 surfaces of the joint. The outer sheath is strong in front, where 

 it is firmly united to the extensor tendon. Behind, the capsule 

 is distended so as to form a kind of blind sac (fig. 10,//'), which 

 extends upwards behind the coronet bone. At this point its 

 outer sheath is very thin, but between the navicular and pedal 

 bones it is strengthened by fibres which run from before back- 

 wards, and w^hich are so well-marked as to present the appear- 

 ance of a special ligament, w^hich has been described as the 

 inferior navicular ligament or interosseous ligament. 



(h) The coronet and pedal bones are connected by an inner 

 and an outer lateral ligament {i) (antero-lateral ligaments, 

 MTadyean). These ligaments are excessively strong ; they arise 

 from the ligamentous furrow at the sides of the coronet bone, 

 run somewhat obliquely backwards and downwards to end in 

 special pits on the upper border of the pedal bone, flanking 

 on either side the pyramidal process. Posteriorly, they are 

 bounded by the lateral cartilages, in the tissues of which they 

 are lost. 



(c) The navicular bone is connected with the suffraginis 

 and pedal bones and wdth the lateral cartilages. 



With the suffraginis bone by means of the postero-lateral 

 ligaments or suspensory ligaments of the navicular bone {k, 



