rformance of slight lateral movements. It is formed by the opposing of
the inferior surface of the os suffraginis with the superior surface of the
os coronae. The articulating surface of the os coronae is supplemented by
the addition behind of a thick piece of _fibro-cartilage (the glenoid_)
attached inferiorly to the posterior edge of the upper articulatory surface
of the os coronae, and superiorly by means of three fibrous slips on each
side to the os suffraginis. The innermost of these three slips becomes
attached to about the middle of the lateral edge of the suffraginis, and
the remaining two, beneath the first, attach themselves to nearer the lower
end of that bone. The posterior surface of the complementary cartilage
forms a gliding surface for the passage of the perforans.

[Illustration: FIG. 6.--THE NAVICULAR BONE (VIEWED FROM BELOW). 1, Inferior
surface (smooth for the passage of the flexor perforans); 2, anterior edge
of inferior surface; 3, posterior edge of inferior surface.]

[Illustration: FIG. 7.--THE NAVICULAR BONE (VIEWED FROM ABOVE, THE BONE
TILTED POSTERIORLY TO SHOW ITS ANTERIOR BORDER). 1, Superior articulatory
surface; 2, anterior border (grooved portion of); 3, anterior border
(articulatory portion of).]

[Illustration: FIG. 8.--LIGAMENTS OF THE FIRST AND SECOND INTERPHALANGEAL
ARTICULATIONS (VIEWED FROM THE SIDE). (AFTER DOLLAR AND WHEATLEY.) 1,
Outermost slip from the glenoidal fibro-cartilage; 2, lateral ligament of
the first interphalangeal articulation; 3, prolongations of the lateral
ligament of the first interphalangeal articulation attached to the end of
the navicular bone to form the postero-lateral ligament of the pedal joint;
4, end of the navicular bone; 5, antero-lateral ligament of the pedal
joint.]

_The Lateral Ligaments_.--These are large and thick, an outer and an inner,
running obliquely from above downwards and backwards. Each is inserted
superiorly into the lateral tubercle of the lower end of the first phalanx,
and inferiorly to the side of the second phalanx, their most inferior
fibres becoming finally fixed to the extremities of the navicular bone,
where they form the postero-lateral ligaments of the pedal articulation.
In front of the joint the extensor pedis plays the part of an additional
ligament.

_The Synovial Membrane_.--This is limited in front by the tendon of the
extensor pedis, on each side by the lateral ligaments of the joint, and
behind by the glenoid fi