Page 148 - Anatomy and Physiology of Farm Animals, 8th Edition

Anatomy of the Muscular System / 133

away from the moving bones and prevent Muscles Acting on the Distal Limb
“pinching” of the tissues between humerus
VetBooks.ir and ulna when the joint is extended. With few exceptions, the extensors of

The m. tensor fasciae antebrachii
originates via a thin aponeurosis that is the carpus and digits take origin from the
lateral epicondyle of the humerus and have
blended with the long head of the triceps muscle bellies that occupy the cranial and
muscle and the m. latissimus dorsi. The lateral parts of the antebrachium (forearm).
flattened muscle belly lies on the caudo­ Likewise, muscles that flex the carpus and
medial aspect of the arm and inserts via a digits take origin from the medial humeral
second aponeurosis on the olecranon and epicondyle and medial aspects of the prox­
antebrachial fascia. The muscle’s name imal radius and ulna; their muscle bellies
reflects its action on the antebrachial fas­ form the bulk of the caudal aspects of the
cia (it tenses it), but through these fascial antebrachium (Fig. 7‐8).
connections the m. tensor fasciae antebra-
chii also assists the triceps in extension of Extensors of the Carpus. The m. extensor
the elbow. carpi radialis is the largest extensor of
the carpus. It extends from the lateral
Flexors of the Elbow. The m. biceps epicondyle of the humerus to the proximal
brachii originates on the supraglenoid end of the metacarpal region where it
tubercle just dorsal and cranial to the inserts on the metacarpal tuberosity on the
articular surface of the scapula. It inserts dorsal surface of the proximal metacarpus.
on (1) the radial tuberosity on the cranial
aspect of the proximal radius, (2) the medial
collateral ligament of the elbow, and (3) the
antebrachial fascia. In horses, the tendinous
blending with the antebrachial fascia forms
a palpable cordlike structure on the flexor
surface of the elbow called the lacertus
fibrosus. The biceps assists in holding
the shoulder joint in apposition and may
assist with extension of that joint. However,
the chief action of the m. biceps brachii is
flexion of the elbow.
The m. brachialis is strictly a flexor of
the elbow since it originates on the humerus a
and inserts on the cranial aspect of the
radius (and in some species the ulna). b
As ungulates have only limited or absent
ability to pronate and supinate their limbs,
the m. pronator teres is reduced to a liga­
ment in horses and only a small, weak
muscle in ruminants and pigs. In these
species, it acts primarily as a weak flexor
of the elbow. It originates on the medial
epicondyle of the humerus and inserts on
the medial side of the radius. Figure 7-8. Muscles that extend the carpus and
Extensor muscles of the carpus and phalangeal joints lie on the cranial aspect of the
digit (discussed in the next section), which antebrachium; muscles that flex these joints lie on
originate on the lateral epicondyle of the the caudal aspect. Two examples are depicted: a,
humerus, may assist in flexion of the common digital extensor m.; b, superficial digital
elbow as a secondary function. flexor m.