Veterinary Gross Anatomy-II

Muscles of the thoracic limb-Horse

MUSCLES OF THE THORAIC LIMB-HORSE

• The variations in the musculature of the horse is given below.
• The anterior superficial pectoral is more distinct than the posterior.
• The deep pectoral is divisible into anterior and posterior divisions. The anterior deep pectoral extends in front of the supraspinatus to the cervical angle of the scapula. The posterior is fan shaped.
• The trapezius is distinctly separable into cervical and dorsal parts by an intermediate aponeurosis.
• The omotransversarius is absent.
• The brachiocephalicus is less distinct in its division into two parts.
• The serratus thoracis and serratus cervicis together form a wide fan-shaped muscle serratus ventralis, which is inserted to the two triangular areas on the medial surface of the scapula.
• The subscapsularis does not present three divisions. It has only one fleshy part.
• The capsularis is a very fine narrow muscle arising just above the posterior part of the rim of the glenoid cavity and is inserted to the posterior part of the neck of the humerus by insinuating itself between the fibres of origin of the brachialis. This muscle raises the capsule of the shoulder joint during flexion of the joint.
• The part of the deltoideus corresponding to the acromial part of the ox arises from the spine of the scapula by means of strong aponeurosis covering the infraspinatus.
• The tendon of origin of the biceps brachii is adapted to the biciptial groove.
• The tensor fascia antibrachii is very wide below. It is inserted to
• Deep fascia of the forearm
• The olecranon.
• The extensor carpi radialis resembles that of the ox.
• The medial digital extensor is absent.
• The extensor pedis or common digital extensor arises in common with the preceding. Its tendon descends in a synovial sheath over the carpus, passes down the metacarpus and at the fetlock. It receives two slips from the suspensory ligament to form the broad ligament, which is inserted to the extensor process of the pedis.
• The lateral digital extensor is smaller. It arises from the humerus and the radius and its tendon is inserted to the prominence on the dorsal aspect of the upper extremity of the first phalanx.
• The extensor carpi obliquus is inserted to the head of the medial small metacarpus bone.
• The pronator teres is usually not present or is represented by a tendinous band.
• The flexors of the metacarpus resemble that of the ox.
• The superficial digital flexor does not divide into two parts. Its tendon is reinforced above the carpus by a strong fibrous band - the superior check ligament. The ring for the deep flexor is formed entirely by the superficial flexor tendon.
• The deep digital flexor presents the same heads. Its tendon receives about half way down the metacarpus the inferior check ligament. It is inserted to the semilunar crest and tendinous surface of the os pedis.

Lumbricales (medialis and lateralis)

• These are two slender bundles arises from the deep flexors tendon and in the fibrous tissue of ergot. They lie on either side of the flexor tendons.

Interossei

• These are three in number and lie in the metacarpal groove.
• Two of these i.e the medialis and lateralis, are very slender, and each arises from the corresponding small metacarpal bone, near its proximal extremity.
• The tendons of these are lost in the fascia at the fetlock.
• The third is the interosseous medius or suspensory ligament.