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 foraminæ 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 horizontally forwards from the angles or wings of
the bone, and terminates anteriorly in one of the larger foraminæ. As the
name 'laminal' indicates, it is this surface which in the fresh state is
covered by the sensitive laminæ.

_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 foraminæ; in this case more minute. In the recent
state it is covered by the sensitive sole. The posterior region, lying
immediately behind the semilunar crest, shows on each side of a median
process a large foramen, the _Plantar Foramen_. From this foramen runs the
_Plantar Groove_, a channel, bounded above by the superior edge, and below
by the semilunar crest of the bone, which conducts the plantar arteries
into the _Semilunar Sinus_, a well-marked cavity in the interior of the
bone.