Page 147 - Anatomy and Physiology of Farm Animals, 8th Edition

132 / Anatomy and Physiology of Farm Animals

The m. latissimus dorsi has been of the support of the trunk and contributes
to stabilization of the shoulder joint.
described above as an extrinsic muscle of
VetBooks.ir the forelimb. Its attachments to the thora­ muscle extending from the coracoid pro­
The m. coracobrachialis is a small
columbar vertebrae and medial humerus
make it a very strong flexor of the shoulder. cess on the medial side of the scapula to the
When the foot is firmly planted on the medial side of the shaft of the humerus.
ground, contraction of the m. latissimus The location of the muscle belly suggests a
dorsi will draw the trunk forward, an shoulder flexor, but its attachments make
important action during gait. this muscle an extensor of that joint.
The m. infraspinatus originates from The m. subscapularis stabilizes the
the infraspinous fossa just caudal and ven­ shoulder on the medial side. It originates
tral to the spine of the scapula. It inserts from the subscapular fossa on the medial
into the caudal part of the greater tubercle side of the scapula below the attachments
of the humerus. The m. infraspinatus also of the m. rhomboideus and m. serratus ven-
acts as a strong collateral ligament of the tralis. It inserts on the lesser tuberosity of
shoulder joint and may abduct, flex, and the humerus and provides some adduction
outwardly rotate the shoulder. This muscle to the shoulder joint.
also atrophies in cases of sweeny.
The m. teres minor lies just distal to the
infraspinatus muscle and has the same Muscles Acting on the Elbow
action as the m. infraspinatus. The m. teres Since the elbow is a hinge joint, the muscles
minor originates from the distal caudal acting on it are either flexors or extensors.
border of the scapula and inserts on the In quadrupeds, the extensors are typically
teres minor tuberosity of the humerus stronger than the flexors because they sup­
just distal to the greater tubercle of the port the weight of the body by maintaining
humerus. the limbs in extension at rest.
The m. deltoideus extends from the
spine of the scapula to the deltoid tuber­ Extensors of the Elbow. The m. triceps
osity of the humerus. It is an abductor and brachii has three heads. The long head
flexor of the shoulder joint. originates from the caudal border of the
scapula, and the medial and lateral heads
Adductors of the Shoulder. The pectoral originate from the respective sides of the
muscles form the substance of the brisket. humeral diaphysis. Carnivores have an
They originate from the sternum and insert accessory head that also originates from
mainly on the proximal part of the humerus. the humerus between the medial and
Commonly, they are divided into the lateral heads (although this arrangement
super ficial pectoral muscle (m. pectoralis gives the carnivore four heads on this
superficialis) and the deep pectoral muscle, it is still called a triceps). All heads
muscle (m. pectoralis profundus). These insert on the olecranon process of the
pectoral muscles are strong adductors of ulna. The triceps is the strongest extensor
the forelimb, and the deep pectoral muscle of the elbow. The long head can also act to
also advances the trunk when the foot is flex the shoulder.
fixed on the ground (weight bearing). The m. anconeus, deep to the m. triceps
The m. subclavius is absent in carnivores, brachii, is a small muscle that covers the
small in ruminants, and well developed in caudal aspect of the joint capsule of the
horses and pigs. It has sometimes been elbow. It also originates on the humerus,
considered part of the deep pectoral muscle. inserts on the olecranon process, and nomi­
The m. subclavius arises from the cranial nally extends the elbow. Because the deep
sternum and costal cartilages and arcs side of the muscle is attached to the elbow
craniodorsad to insert on the deep fascia of joint capsule, it is likely that an important
the m. supraspinatus. This muscle is part function is actually to lift the joint capsule