Page 149 - Anatomy and Physiology of Farm Animals, 8th Edition

134 / Anatomy and Physiology of Farm Animals

This is the most prominent muscle on the origin from the medial epicondyle of the
humerus and inserts on the palmar aspect
front of the forearm and is the most cranial
VetBooks.ir muscle of the group. of the proximal end of the meta carpus
(medial side).
The m. extensor carpi obliquus is a
flat, triangular extensor of the carpus lying On the caudal side of the antebrachium,
deep to the digital extensor muscles of the the m. flexor carpi ulnaris exerts consid­
antebrachium. It arises from the craniolat­ erable leverage as a flexor of the carpus by
eral aspect of the distal half of the radius inserting on the accessory carpal bone,
(and ulna in species with a complete ulna). which projects in a palmar direction from
Its oblique tendon crosses mediad on the the lateral aspect of the carpus.
cranial aspect of the carpus, superficial to
the tendon of the m. extensor carpi radia- Extensors of the Digit. The common
lis, to insert on the most medial metacar­ digital extensor muscle (m. extensor
pal bone, which is the second in the horse, digitorum communis) is the longest
the third in the cow and sheep, and the extensor muscle in the thoracic limb. It
second in pigs. In humans, this muscle is originates from the lateral epicondyle of
one of the well‐developed abductors and the humerus close to the m. extensor carpi
extensors of the thumb (the pollex) and so radialis. Its tendinous insertion is on the
in this species is called the m. abductor extensor process of the distal phalanx and
pollicis longus. This name is only infre­ on the proximal ends of the middle and
quently used in veterinary anatomy, since proximal phalanges. The tendon is single
most domestic species lack a well‐devel­ in the horse; double in the cow, sheep, and
oped first digit. Another synonym for the goat; and split into four separate tendons
same muscle is m. abductor digiti I, a name in the pig and carnivores, in which species
that likewise reflects its function as an it inserts on the second through the fifth
abductor of the first digit. digits. This muscle is an extensor of all
The m. extensor carpi ulnaris (formerly joints of the digit, including the metacar­
m. ulnaris lateralis) is the most caudal of pophalangeal (fetlock) joint. It may also
the extensor muscles. It also takes origin assist in extending the carpus and even in
from the lateral epicondyle of the humerus, flexing the elbow (owing to its origin on
but passes downward over the lateral side the humerus).
of the carpus to insert on the most lateral The common digital extensor m. of
metacarpal bone and on the accessory animals with more than a single digit has
carpal bone. In spite of its official name, several distinct heads. In ruminants, one
this muscle in ungulates probably produces of these heads gives rise to its own tendon
variable amounts of flexion at the carpus, that inserts on the third digit (the medial
although by origin and nerve supply it toe). This head of the common digital
belongs with the extensor group (for this extensor m. is sometimes identified as a
reason, many veterinary anatomists rec­ separate muscle, the medial digital exten­
ommend the alternate name, m. ulnaris sor muscle.
lateralis). The lateral digital extensor m.
In addition to these carpal extensors, (m. extensor digitorum lateralis) is found
the extensor muscles of the digits whose in all species. Its origin is just caudal to the
tendons pass over the dorsal surface of the common digital extensor m. on the lateral
carpus may act secondarily as extensors of collateral ligament of the elbow and lateral
the carpus. radius and ulna. The insertion varies accord­
ing to the number of digits present, and
Flexors of the Carpus. On the medial there are interspecific differences regarding
side of the forearm, the m. flexor carpi to which phalanx the tendon attaches. In
radialis is just caudal to the radius, which pigs it inserts on the fourth and fifth digits;
is palpable directly beneath the skin. It takes in ruminants, on the middle phalanx of the