_1_, Large metacarpal bone; _3_, fetlock joint; _4_, proximal sesamoid
bone; _5_, first phalanx; _6_, pastern joint; _7_, second phalanx;
_8_, coffin joint; _9_, third phalanx; _10_, distal sesamoid
(navicular bone); _12_, suspensory ligament; _14_, deep flexor
tendon; _15_, superficial flexor tendon; _16_, posterior annular
ligament of fetlock; _20_, inferior sesamoidean ligaments; _21_,
extensor tendon; _24_, plantar cushion; _25_, periople; _28_, wall
of hoof; _29_, sole of hoof; _A_, navicular bursa, proximal part.
(After Ellenberger-Baum, Anat. für Künstler.)
]
[Illustration:
FIG. 149.—ARTICULAR SURFACES OF FIRST PHALANX AND SESAMOIDS AT
FETLOCK, WITH INTERSESAMOID AND SUSPENSORY LIGAMENTS. (After
Schmaltz, Atlas d. Anat. d. Pferdes.)
]
The =joint capsule= is attached around the margin of the articular
surfaces. It is thick and ample in front; here a bursa is interposed
between it and the extensor tendons, but the tendons are also attached
to the capsule. Posteriorly it forms a thin-walled pouch which extends
upward between the metacarpal bone and the suspensory ligament about as
high as the point of bifurcation of the latter. The capsule is
reinforced by two lateral ligaments.
The =lateral ligaments=, =external= and =internal= (Ligamentum
collaterale ulnare, radiale) are partially divided into two layers: the
=superficial layer= arises from the eminence on the side of the distal
end of the large metacarpal bone, and passes straight to the rough
lateral area below the margin of the articular surface of the first
phalanx; the =deep layer=, shorter and much stronger, arises in the
lateral depression on the distal end of the metacarpal bone, and passes
obliquely downward and backward to be inserted into the outer surface of
the sesamoid and the proximal end of the first phalanx.
The capsule is further strengthened by a layer of oblique fibers which
pass over the lateral ligament on either side and end on the extensor
tendon and the proximal extremity of the first phalanx. It may
properly be regarded as fascia rather than ligament.
[Illustration: