12 DISEASES OF THE HORSE'S FOOT 



The Navicular Bone, Shuttle Bone, or Small Sesa- 

 moid. — Placed behind the articulating point of the second 

 and third phalanges, this small shuttle-shaped bone assists 

 in the formation of the pedal articulation. It is elongated 

 transversely, flattened from above to below, and narrow at 

 its extremities. In it we see two surfaces, and two borders. 



The Superior or Articular Surface of the bone, which 

 may easily be recognised by its smoothness, is moulded upon 

 the lower articular surface of the second phalanx, being 

 convex in its middle, and concave on either side. 



The Inferior or Tendinous Surface resembles the pre- 

 ceding in form, but is broader and less smooth. In the 

 recent state it is covered with fibro-cartilage for the passage 

 of the flexor perforans. 



The Anterior Border possesses above a small trans- 

 versely elongated facet for articulation with the os pedis, 

 and below a more extensive grooved portion, perforated by 

 numerous foramina^, affording attachment to the inter- 

 osseous ligaments of the articulation. 



The Posterior Border, thick in the middle, but thinner 

 towards the extremities, is roughened for ligamentous 

 attachment. 



Development. — The bone ossifies from a single centre. 



B. THE LIGAMENTS. 



The Articulation of the First with the Second 

 Phalanx, or the Pastern Joint. — Adhering to the limit 

 we have set, this articulation should not receive our atten- 

 tion. As, however, we shall in a later page be concerned 

 with fractures of the os coronse, which fractures may affect 

 the articulation above mentioned, a brief note of its forma- 

 tion will not be out of place. 



It is an imperfect hinge-joint, permitting of extension and 

 flexion, allowing the first phalanx to pivot on the second, 

 and admitting of the performance of slight lateral move- 

 ments. It is formed by the opposing of the inferior surface 

 of the os suffraginis with the superior surface of the os 

 coronse. The articulating surface of the os coronae is 



