Muscles of the Equine Thoracic Limb
Muscle Origin Insertion Innervation Action
Deltoideus m. Spine of the Scapula
&
Caudal Border of Scapula
Deltoid Tuberosity of Humerus Axillary n. Flexes shoulder
Supraspinatus m. Supraspinatous Fossa
&
Scapular Cartilage and Spine
Greater and Lesser Tubercles of Humerus Suprascapular n. Extends shoulder

Stabilizes shoulder

Infraspinatus m. Infraspinatous Fossa
&
Scapular Cartilage and Spine
Greater Tubercle of Humerus Suprascapular n. Extends and flexes shoulder
Teres minor m. Distal Half of Caudal Border of Scapula Deltoid Tuberosity of Humerus Axillary n. Flexes shoulder
Triceps brachii m.  
long head Caudal Border of Scapula Olecranon Tuber Radial n. Extends elbow

Flexes shoulder

lateral head Deltoid Tuberosity Olecranon Tuber Radial n. Extends elbow
medial head Medial Surface of Middle 1/3 of Humerus Olecranon Tuber Radial n. Extends elbow
Anconeus m. Border of Olecranon Fossa Lateral Olecranon Radial n. Extends elbow

Raises joint capsule to prevent capsule's compression during extension of elbow

Teres major m. Caudal Border of Scapula
&
Subscapularis
Teres Tuberosity of Humerus Axillary n. Flexes shoulder
Subscapularis m. Subscapular Fossa of Scapula Lesser Tuberosity of Humerus Subscapular and Axillary n. Extends shoulder
Coracobrachialis m. Coracoid Process of Scapula Proximomedial Surface of Humerus Musculocutaneous n. Extends shoulder

Adducts limb

Biceps brachii m. Supraglenoid Tubercle Radial Tuberosity
&
Tendon of Extensor Carpi Radialis m. (via Lacertus Fibrosis)
Musculocutaneous n. Extends shoulder

Flexes elbow (via Lacertus Fibrosis)

Stabilizes carpus (via tendon of extensor carpi radialis m.)

Brachialis m. Proximocaudal Surface of Humerus Proximomedial Surface of Radius Musculocutaneous n.
(Radial n. innervates lateral side in many horses)
Flexes elbow
Tensor fascia   antebrachii m. Caudal Border of Scapula Deep Fascia of Forearm
&
Olecranon
Radial n. Extends elbow

Tenses forearm fascia

Common digital extensor m.
includes Medial digital extensor m.
Lateral Epicondyle of Humerus Proximodorsal on Proximal Phalanx
&
Extensor Processes of Middle and Distal Phalanges
Radial n. Extends carpus

Extends digit III

Lateral digital extensor m. Proximal Radius and Ulna Proximodorsal on Proximal Phalanx Radial n. Extends metacarpophalangeal joint
(Fetlock)
Extensor carpi radialis m. Lateral Supracondylar of Humerus Proximodorsal on Metacarpal III Radial n. Extends carpus
Ulnaris lateralis m. Lateral Epicondyle of Humerus Accessory Carpal Bone
&
Metacarpal IV
(Lateral Splint Bone)
Radial n. Flexes carpus
Extensor carpi obliquus m.
(Abductor pollicis longus m.)
Middle of Radius, Craniolaterally Proximal Metacarpal II
(Medial Splint Bone)
Radial n. Extends carpus
Superficial digital flexor m.
superficial and deep parts
Medial Epicondyle of Humerus Distal Collateral Tubercles of Proximal Phalanx
&
Proximal Collateral Tubercles of Middle Phalanx
Ulnar n. Extends elbow

Flexes carpus

Flexes digit

Deep digital flexor m.  
humeral head Medial Epicondyle of Humerus Flexor Surface of Distal  Phalanx Median n.
&
Ulnar n.
Extends elbow

Flexes carpus

Flexes digit

ulnar head Medial Olecranon Ulnar n.
radial head Middle of Radius, Caudal Surface Median n.
Flexor carpi ulnaris m.  
humeral head Medial Epicondyle of Humerus Accessory Carpal Bone Ulnar n. Flexes carpus
ulnar head Medial Olecranon Accessory Carpal Bone Ulnar n. Flexes carpus
Flexor carpi radialis m. Medial Epicondyle of Humerus Proximal Sesamoid Bones Median n. Flexes carpus
Interosseous Proximocaudal on Metacarpal III
&
Palmer Carpal Ligament
Proximal Sesamoid Bones Deep Branch of Ulnar n. Resists overextension of metacarpophalangeal joint
(Fetlock)