l 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
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 foraminae, affording attachment to the
interosseous 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 attention. As, however, we shall in a later page be concerned
with fractures of the os coronae, which fractures may affect the
articulation above mentioned, a brief note of its formation 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
pe