Page 157 - Anatomy and Physiology of Farm Animals, 8th Edition

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Extensors of the Stifle. One large m. semitendinosus, which also assist in
extending the hock and hip and flexing
muscle, the m. quadriceps femoris, is the
VetBooks.ir primary extensor of the stifle. This muscle the stifle. The deep digital flexor m. also
extends the hock.
has four heads; their distinct origins and
clearly distinguishable muscle bellies
make it common practice to name them as Flexors of the Hock. Flexors of the
separate muscles. The longest head, the hock include the m. tibialis cranialis
m. rectus femoris, originates from the and the various fibular (formerly peroneal)
ilium just above the acetabulum. The other muscles, whose tendons pass over the
three heads, m. vastus medialis, m. vastus dorsal surface of the hock to insert on the
intermedius, and m. vastus lateralis, tarsus and metatarsus. The m. fibularis
originate from the respective areas of the tertius (formerly peroneus tertius) is the
shaft of the femur. All four heads insert only named fibular muscle in the horse.
on the patella. The patella, being fastened Additionally, the m. fibularis longus is
to the front of the tibia by the patellar found on the ox, sheep, goat, pig, and dog.
ligaments, extends the stifle when it is The m. fibularis brevis is found only in
pulled proximad by the m. quadriceps carnivores and humans. The digital
femoris. Because of its origin on the ilium, extensors also flex the hock, because their
the m. rectus femoris also flexes the hip. tendons pass over its flexor surface.
Flexors of the Stifle. The chief flexors of
the stifle are the hamstring muscles, which Muscles Acting on the Digit
also extend the hip (m. biceps femoris,
m. semitendinosus, m. semimembranosus; Digital extensors of the thoracic limb are
discussed earlier). In addition, the extensor also able to extend the carpus, but digital
muscles of the hock that originate on the extensors of the pelvic limb produce flex­
caudal surface of the distal end of the ion at the hock. Likewise, digital flexors
femur may also flex the stifle. These of the thoracic limb produce flexion of
muscles include the m. gastrocnemius and the carpus, while digital flexors of the
the superficial digital flexor m. (discussed pelvic limb produce extension the hock
later). The m. popliteus is a relatively small (Fig. 7‐11). Muscles acting on the digits of
muscle caudal to the stifle. Its chief action the pelvic limb are similar in attachments
is flexion of the stifle, although it may and locations to those of the thoracic limb.
slightly rotate the leg (tibia and fibula)
mediad. Extensors of the Digit. The long digital
extensor muscle (m. extensor digitorum
longus) originates from the distal end of
Muscles Acting on the Hock the femur and passes distad to insert on
the distal phalanx of each digit. As with the
The principal actions of the hock are exten­ common extensor in the thoracic limb, the
sion and flexion. tendon has one part in the horse; two parts
in the ox, goat, and sheep; and four parts in
Extensors of the Hock. Extensors of the pig and carnivores.
the hock primarily attach to the calcaneus The lateral digital extensor muscle
(point of the hock) by way of the common (m. extensor digitorum lateralis) lies
calcanean tendon. The m. gastrocnemius between the extensor and flexor groups of
and superficial digital flexor m. muscles of the crus. In the horse, its tendon
originate from the caudal aspect of the joins that of the long digital extensor m. at
distal femur, and their tendons make up about the middle of the cannon. In rumi­
the bulk of the common calcanean tendon. nants, it inserts via a separate tendon on
They are joined in part by portions of the proximal middle phalanx of the fourth
the m. biceps femoris, m. gracilis, and digit. In pigs, it resembles the ruminant