_The Superior or Articular Surface_ consists of two shallow depressions,
divided by a slight median ridge. Its posterior part shows a transversely
elongated facet for articulation with the navicular bone.

_The Superior Edge_, outlining the superior margin of the laminal surface,
describes a curve, with the convexity of the curve forward. In the centre
of the curve is a triangular process, the _Pyramidal Process_, which serves
as the point of attachment of the extensor pedis.

_The Inferior Edge_, the most extensive of the three, separates the laminal
from the solar surface. It is semicircular in shape, sharp, and finely
dentated, and is perforated by eight to ten large foraminæ.

_The Posterior Edge_, very slightly concave, divides the small,
transversely elongated facet of the superior surface from the posterior
region of the inferior surface.

_The Lateral Angles_ of the bone, also termed the _Wings_, are two
projections directed backwards. Each is divided by a cleft into an upper,
the _Basilar Process_, and a lower, the _Retrossal Process_. In old animals
the posterior portion of the cleft separating the two processes gradually
becomes filled in with bony deposit, thus transforming the cleft into a
foramen, which gives passage to the preplantar artery. We may mention
in passing that the lateral angles give attachment to the lateral
fibro-cartilages, and that the lateral angles themselves in old horses
become increased in size owing to ossification of portions of the adjacent
lateral cartilages.

_Development_.--The os pedis ossifies from two centres, one of which is for
the articular surface; but this epiphysis fuses with the rest of the bone