=Ox.=—The two proximal joints have separate capsules, and broad, but
rather indistinct, lateral ligaments. Each joint has also two central
and two lateral volar ligaments. The central ligaments are largely fused
to form a strong band. The lateral ones extend from the borders of the
first phalanx to the proximal end of the second phalanx.
The distal interphalangeal joints have, in addition to the capsules and
lateral ligaments, bands which reinforce them on either side. The
central or interdigital pair arise in the depressions on the distal ends
of the first phalanges, receive fibers from the second phalanges, and
end on the interdigital surfaces of the third phalanges at the margin of
the articular surface. The lateral pair have a similar course, but are
thinner, and end on the corresponding third sesamoid. An elastic band
crosses the front of the second phalanx obliquely, from the distal end
of the first phalanx to the extensor process of the third phalanx.
The =crucial= or =inferior interdigital ligaments= (Ligamenta cruciata
interdigitalia) are two strong bands which limit the separation of the
digits. They are attached above to the lateral (or abaxial) eminences on
the proximal ends of the second phalanges (blending with the lateral
ligaments), cross the deep flexor tendon obliquely, and reach the
interdigital space, where they intercross and blend. Most of the fibers
end on the third sesamoid of the opposite side, but some are attached to
the interdigital aspect of the second phalanx and the third sesamoid of
the same side. In the sheep there is, instead of the foregoing, a
transverse ligament which is attached on either side to the interdigital
surfaces of the second and third phalanges and the third sesamoid bone.
It is related below to the skin, above to a pad of fat.
=Pig.=—The interphalangeal joints of the chief digits resemble in
general those of the ox. The inferior interdigital ligament resembles,
however, that of the sheep, and is intimately adherent to the skin.
There is, besides, a remarkable arrangement of ligaments which connect
the small digits with each other and with the chief digits.
This apparatus is somewhat complex, but its chief features are as
follows: A superior interdigital ligament is attached on either side
to the third phalanges of the small digits, while centrally it blends
with the annular ligaments of the flexor tendons behind the
metacarpo-phalangeal joints of the chief digits. Two bands (central
longitudinal interdigital ligaments) arise on the bases of the small
digits, cross the flexor tendons obliquely downward and inward, pass
through the superior interdigital ligament, and blend below with the
inferior interdigital ligament. Two lateral bands (lateral
longitudinal interdigital ligaments) are attached in common with the
superior interdigital ligaments to the third phalanges of the small
digits, and blend below with the outer part of the inferior
interdigital ligament.
=Dog.=—Each joint has a capsule and two lateral ligaments. The distal
joints have also two elastic =dorsal ligaments= (Ligamenta dorsalia),
which extend from the proximal end of the second phalanx to the ridge at
the base of the third phalanx (Fig. 133). They produce dorsal flexion of
the joint, and thus raise or retract the claws when the flexor muscles
relax. The distal sesamoids are represented by complementary cartilages
attached to the volar margins of the articular surfaces of the third
phalanges.
Three interdigital ligaments restrict the spreading apart of the digits.
Two of these cross the volar surface of the proximal parts of the chief
digits, _i. e._, one for the second and third, the other for the fourth
and fifth; they blend with the annular ligaments on either side. The
third ligament is attached on either side to the foregoing ligaments and
the annular ligaments of the third and fourth digits, and curves
downward centrally, ending in the large pad on the paw.