View source for Intrinsic Musculature of the Thoracic Limb- Horse Anatomy

===Intrinsic Musculature===

====Muscles of the Shoulder====

These muscles are grouped:

====='''Lateral'''=====

'''''Supraspinatus '''''
:'''Innervation''':Suprascapular n. of the brachial plexus
:'''Origin''': Supraspinous fossa of the scapula
:'''Insertion''': Lesser and greater tubercles of the humerus
:'''Action''': Extends and braces the shoulder

'''''Infraspinatus'''''
:'''Innervation''':Suprascapular n. of the brachial plexus
:'''Origin''': Supraspinatous fossa and spine of the scapula
:'''Insertion''': Tendon of insertion bifurcates into a deep part and a superficial part.
:: Deep - Greater tubercle of the humerus 
:: Superficial - Lateral humerus, distal to the greater tubercle
:'''Action''': Brace the shoulder, supporting flexion or extension. 
:'''Clinical significance''': The bursa between the superficial tendon of the infraspinatus, and the lateral tubercle of the humerus can be the site of inflammation (bursitis).

====='''Medial'''=====

'''''Supscapularis'''''
:'''Innervation''': Subscapular n. from the brachial plexus
:'''Origin''': Deep surface of the scapula
:'''Insertion''': Lesser tubercle of the humerus
:'''Action''': Braces medial shoulder joint. Primarily acts as an extensor of the shoulder, but can contribute to maintaining flecion. 

'''''Coracobrachialis'''''
:'''Innervation''': Musculocutaneous n. of the brachial plexus
:'''Origin''': Coracoid process of scapula
:'''Insertion''': Proximal shaft of the humerus
:'''Action''': Fixator

====='''Caudal (Flexors)'''=====

'''''Deltoid'''''
:'''Innervation''': Axillary n. of the brachial plexus
:'''Origin''': Caudal border and spine of the scapula. One head in the horse, compared with two in species with an acromion (site of second origin.
:'''Insertion''': Deltoid tuberosity of humerus
:'''Action''': Flexes shoulder
:In the horse, the aponeurosis of the deltoid is partially fused to the ''infraspinatus''.

'''''Teres Major'''''
:'''Innervation''': Axillary n. of the brachial plexus
:'''Origin''': Dorsal part of the caudal scapula
:'''Insertion''': Teres major tuberosity midway down the humerus
:'''Action''': Flexes the shoulder, supports adduction.

'''''Teres Minor''''' 
:'''Innervation''': Axillary n. of the brachial plexus
:'''Origin''': Distal third of scapula, deep to the deltoid
:'''Insertion''': Teres minor tuberosity midway down the humerus
:'''Action''': Flexes the shoulder

NB// There are no defined extensors of the shoulder. Those involved (brachiocephalic m., biceps brachii, supraspinatus, and ascending pectorals) have other, more primary roles.


[[Category:Horse Anatomy]]