142 THE CONDITION OF HUNTERS 



weight being received from the pastern, the navicular 

 bone descends with the pressure, inclining backwards, 

 conveying the weight to the fatty frog, and thereby 

 acting as a powerful spring to all that portion of the 

 foot which is posterior to the coffin bone. On inspec- 

 tion of this joint, in its healthy state, the navicular 

 bone (which forms the joint with the flexor tendon, by 

 a corresponding convexity in the centre of the bone) 

 presents an exquisitely polished surface, resembling 

 a shell, though at the same time it is highly vascular, 

 and has the power of secreting that phenomenon in 

 animal economy, synovia, or joint oil,^ by which the 

 joints are lubricated when in action. 



Now it appears most clearly that there are two 

 distinct causes for the disease of the navicular joint 

 — one, from any effectual opposition it may meet with 

 in its descent, as above described (and which descent, 

 as it receives the weight perpendicularly, and not 

 obliquely, as with the coffin bone, is essential to prevent 

 concussion) ; and the other, by inflammation, which 

 attacks the synovial membrane which lines the joint 

 and which may proceed from various causes ; though 

 I should imagine concussion, or jar to the foot, to be 

 the principal one ; notwithstanding, to oppose con- 

 cussion to a certain extent, seems to be the principal 

 intention of the parts in question. 



From the information Mr Turner was so kind as to 

 afford me, and from the specimens he presented me 

 with, I am enabled to form the following notions of 



^ The tendons expand at the point to form a sheath — the navicu- 

 lar bursa. 



