_a_, Peroneus tertius; _b′_, tendon of anterior or long extensor; _e_,
deep digital flexor; _e′_, tendon of _e_; _e″_, branch of _h_ to
superficial flexor tendon; _f_, gastrocnemius; _g_, tendon of
superficial digital flexor; _h_, interosseus medius or suspensory
ligament; _i_, annular ligaments; _l_, branch of _h_; _m_, long
digital flexor; _o_, popliteus; _20_, patella; _28_, tuberosity of
tibia. (After Ellenberger-Baum, Anat. für Künstler.)
]
2. The =internal digital extensor= (M. extensor digiti tertii proprius)
arises in common with the preceding muscle and the peroneus tertius, and
is covered by them to the distal third of the tibia. Its tendon passes
under the annular ligaments between those of its cogeners and ends on
the second phalanx of the inner digit.
3. The =lateral digital extensor= (M. extensor digitalis lateralis s.
digiti quarti proprius) arises on the external lateral ligament of the
stifle joint and the external condyle of the tibia. Its tendon passes
over the outer surface of the hock, and terminates on the anterior
surface of the second phalanx of the external digit.
The reinforcing bands from the suspensory ligament are arranged as in
the fore limb.
4. The =extensor brevis= resembles that of the horse, but is inserted on
the tendon of the anterior extensor only.
The =peroneus longus= (not present in the horse) is situated in front of
the lateral extensor. It arises on the external condyle of the tibia and
the fibrous band which represents the shaft of the fibula. Its tendon
passes downward and backward over the outer surface of the hock, crosses
over that of the lateral extensor and under the lateral ligament, and
ends on the first tarsal bone (Cuneiform parvum). It is enveloped by a
synovial sheath. It would apparently act as an inward rotator at the
hock joint.
[Illustration:
FIG. 224.—DISTAL PART OF LIMB OF OX WITH SYNOVIAL SHEATHS AND BURSÆ
INJECTED, ANTERIOR VIEW.
_1_, Tendon of extensor digiti tertii, with bursa (_1′_); _2_, tendon
of anterior extensor; _2′_, branch of _2_, with synovial sheath
(_2″_); _3_, tendon of extensor digiti quarti, with bursa (_3′_);
_a_, metatarsus; _b_, first phalanx; _c_, second phalanx. (After
Schmidtchen.)
]
[Illustration:
FIG. 225.—DISTAL PART OF LIMB OF OX WITH SYNOVIAL SHEATHS INJECTED,
POSTERIOR VIEW.
_1_, Superficial flexor tendon; _1′_, _1′_, branches of _1_; _1″_,
_1‴_, upper part of synovial sheaths of _1′_, _1′_; _2_, deep flexor
tendon; _2′_, _2″_, branches of _2_; _2″_, upper part of synovial
sheath of _2′_; _3_, _3_, lateral branches of interosseus medius or
suspensory ligament; _3′_, branch of same to superficial flexor
tendon; _a_, fetlock joint; _b_, pastern joint; _c_, coffin joint;
_d_, _e_, annular ligaments; _f_, crucial interdigital ligament.
(After Schmidtchen.)
]
The =peroneus tertius= is a well-developed muscle which arises on the
common tendon with the long and internal extensors. It has a large,
fusiform belly, which is superficially situated on the front of the leg.
Close to the tarsus it ends on a flat tendon, which is perforated by
that of the tibialis anterior, and ends on the large metatarsal and
second and third (fused) tarsal bones (Cuneiform magnum).
The =tibialis anterior= is smaller, and arises by two heads. The larger
head springs from the outer surface of the tuberosity of the tibia; the
outer, smaller one (M. extensor hallucis longus), from the upper part of
the external border of the tibia and the fibrous band which replaces the
shaft of the fibula. The tendon perforates that of the preceding muscle
and ends on the metatarsal and second and third tarsal bones.