before birth.

[Illustration: FIG. 4.--THIRD PHALANX OR OS PEDIS (POSTERO-LATERAL VIEW).
1, Anterior or laminal surface; 2, preplantar foramen; 3, preplantar
groove; 4, basilar process of the wing; 5, retrossal process of the wing;
6, foramen caused by the ossifying together posteriorly of the basilar and
retrossal processes.]

[Illustration: FIG. 5.--THIRD PHALANX OR OS PEDIS (VIEWED FROM BELOW). 1,
Plantar surface; 2, plantar foramen and plantar groove; 3, semilunar crest;
4, tendinous surface; 5, retrossal processes of the wings.]

THE NAVICULAR BONE, SHUTTLE BONE, OR SMALL SESAMOID.--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 preceding 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 transversely elongated facet
for articulation with the os pedis, and below a more extensive grooved
portion, perforated by numerous foraminæ, affording attachment to the