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The teres minor muscle originates from the posterior axillary boarder of the scapula and inserts through the capsule of the shoulder joint, and the lower facet of the greater tuberosity of the humerus.It also laterally rotates and abducts the arm. As a rotator cuff muscle, infraspinatus draws the humerus towards the glenoid fossa, thus resisting posterior dislocation of the arm. The tendon of the infraspinatus passes posteriorly on to the glenohumeral join and inserts on to the middle facet of the greater tuberosity of the humerus and capsule of the shoulder joint. It is fractured or luxated most often when the bird has a frontal collision with an object. It opposes the powerful contraction of the major pectoral muscle during the downstroke of the wing. Infraspinatus muscle originates and sits in the infraspinous fossa of the scapula. The coracoid is a stout strong bone that connects the cranial edge of the sternum to the shoulder joint complex.It also prevents deltoid from forcing the humerus up against the acromion.
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The supraspinatus muscle weakly flexes the arm, aids deltoid in abduction of the arm and draws the humerus toward the glenoid fossa. The muscle passes as a tendon under the acromion, where its is separated from the bone by a subacromial bursa and then passes over the glenohumeral joint and inserts on the superior facet of the greater tubercle. The supraspinatus muscle originates and sits in the supraspinatus fossa of the scapular.The rotator cuff mechanism also helps keep the shoulder joint stable by holding the humeral head in the glenoid socket. These 4 muscles are involved in raising the arm from the side and rotating the shoulder in the many directions. The rotator cuff tendons attach to the deep rotator cuff muscles.The serratus anterior pulls the scapula forward of the the thoracic wall and rotates the scapula for abduction and flexion of the arm. They then form a flattened sheet which passes around the thoracic wall and attaches to the anterior (costal surface, that glides over the ribs) of the medial border of the scapula. Serratus anterior muscle originates as a number of muscular slips from the outer surfaces and superior borders of the first eight or nine ribs, and fascia covering the first intercostal spaces (spaces between each rib).Side ( lateral) muscles of the shoulder:.