EEGIONAL ANATOMY 9 



gliding surface for the passage of the flexor perforans ; 

 two lateral surfaces, each rough and perforated by foraminae, 

 and each bearing on its lower portion a thumb-like imprint 

 for ligamentous attachment, and for the insertion of the 

 bifid extremity of the perforatus tendon ; a superior surface, 

 bearing two shallow articular cavities, separated by an 

 antero-posterior ridge, for the accommodation of the lower 

 articulating surface of the first phalanx; an inferior surface, 

 also articulatory, which in shape is obverse to the superior, 

 bearing two unequal condyles, separated by an ill-defined 

 antero-posterior groove, which surface articulates with the 

 OS pedis and the navicular bone. 



Development. — The bone usually ossifies from one centre, 

 but often there is a complementary nucleus for the upper 

 surface. 



The Third Phalanx, Os Pedis, or Coffin Bone. — This 

 also belongs to the class of short bones. It forms the 

 termination of the digit, and, with the navicular bone, is 

 included entirely within the hoof. For our examination it 

 offers three surfaces, two lateral angles, and three edges. 



The Anterior or Laminal Surface, following closely in 

 contour the wall of the hoof, is markedly convex from side 

 to side, nearly straight from above to below, and closely 

 dotted with foraminae of varying sizes. On each side of 

 this surface is to be seen a distinct groove, the preplantar 

 groove, or preplantar fissure, which, commencing behind, 

 between the basilar and retrossal processes, runs hori- 

 zontally forwards from the angles or wings of the bone, and 

 terminates anteriorly in one of the larger foraminae. As 

 the name ' laminal ' indicates, it is this surface which in 

 the fresh state is covered by the sensitive laminae. 



The Inferior or Plantar Surface, hollowed in the form of 

 a low arch, presents for our inspection two regions, an 

 anterior and a posterior, divided by a well-marked line, the 

 Semilunar Crest, which extends forward in the shape of a 

 semicircle. The anterior region, as is the laminal surface, 

 is covered with foraminae ; in this case more minute. In 

 the recent state it is covered by the sensitive sole. The 



