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The muscles of pectoral girdle
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Deltoid (m. deltoideus /дельтовидная мышца)
· Origin. From the lateral third of the clavicle, the acromion and the spine of the scapula.
· Insertion. To the deltoid tuberosity of the humerus.
· Actions. Abduction of the upper limb (assisted by supraspinatus and serratus anterior), flexion (anterior fibres) and extension (posterior fibres) of the arm.
· Nerve supply. Axillary nerve.
Teres major (m. teres major /большая круглая мышца)
· Origin. The lower angle of the scapula.
· Insertion. The medial lip of the intertubercular sulcus.
· Actions. Adduction and medial rotation of the arm.
· Nerve supply. Lower subscapular nerve.
Subscapularis (m. subscapularis /подлопаточная мышца)
· Origin. The subscapular fossa.
· Insertion. Passes in front of the shoulder joint to the lesser tubercle of the humerus.
· Action. Medial rotation of the arm.
· Nerve supply. Subscapular nerves.
Supraspinatus (m. supraspinatus /надостная мышца)
· Origin. The supraspinous fossa.
· Insertion. The top of the greater tubercle of the humerus.
· Action. Initiates abduction of the arm.
· Nerve supply. Suprascapular nerve.
Infraspinatus (m. infraspinatus /подостная мышца)
· Origin. The infraspinous fossa.
· Insertion. The back of the greater tubercle of the humerus.
· Action. Lateral rotation of the arm.
· Nerve supply. Suprascapular nerve.
Teres minor (m. teres minor /малая круглая мышца)
· Origin. The lateral border of the scapula.
· Insertion. The humerus below infraspinatus.
· Action. Lateral rotation of the arm.
· Nerve supply. Axillary nerve.
The muscles of the arm
The anterior group
Coracobrachialis (m. coracobrachialis /клювовидно-плечевая мышца)
· Origin. From the coracoid process along with the short head of biceps.
· Insertion. To the medial side of the humerus.
· Action. Moves the arm upwards and medially.
· Nerve supply. Musculocutaneous nerve.
Biceps brachii (m. biceps brachii/двуглавая мышца плеча)
· Origin. Long head from the supraglenoid tubercle and short head from the coracoid process (with coracobrachialis).
· Insertion. To the radial tuberosity and, via the bicipital aponeurosis, into the deep fascia of the forearm.
· Actions. Flexion and supination of the arm and the forearm.
· Nerve supply. Musculocutaneous nerve.
Brachialis (m. brachialis /плечевая мышца)
· Origin. From the front of the lower part of the humerus.
· Insertion. The tuberosity of ulna.
· Action. Flexion of the elbow.
· Nerve supply. Musculocutaneous nerve and radial nerve.
The posterior group
Triceps (m. triceps brachii /трехглавая мышца плеча)
· Origin. Three heads: long from the infraglenoid tubercle, lateral from the humerus above the spiral line, and medial from the back of the lower part of the humerus.
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· Insertion. The olecranon.
· Action. Extensor of the elbow.
· Nerve supply. Radial nerve.
Anconeus (m. anconeus /локтевая мышца)
· Origin. From the lateral epicondyle of the humerus.
· Insertion. The proximal one fourth of the posterior surface of ulna.
· Action. Extensor of the elbow.
· Nerve supply. Radial nerve.
The fasciae of the arm
· The axillary fascia (fascia axillaris /подмышечная фасция) forms the floor of the axillary fossa.
· The deltoid muscle is covered by a thin deltoid fascia (fascia deltoidea /дельтовидная фасция). This fascia is continuous anteriorly with the pectoral fascia and posteriorly with the superficial fascia of the back. Distally it blends with the brachial fascia.
· The brachial fascia (fascia brachii /фасция плеча) forms a tubular investment for the muscles of the arm.
On both sides the brachial fascia gives off two fibrous intermuscular septa:
- The medial intermuscular septum of arm (septum intermusculare brachii mediale /медиальная межмышечная перегородка плеча) passes between the brachial and coracobrachial muscles, and the triceps muscle and attaches to the medial supracondylar ridge of the humerus.
- The lateral intermuscular septum of arm (septum intermusculare brachii laterale / латеральная межмышечная перегородка плеча) passes between the brachial and brachioradialis muscles and the triceps muscle and attaches to the lateral supracondylar ridge of the humerus.
· In the bend of the arm the fascia is continuous with the antebrachial fascia and has a thickened band here, which is part of the tendon of the biceps brachii, bicipital aponeurosis (aponeurosis m. bicipitis brachii /апоневроз двуглавой мышцы плеча).
The topography of the arm
The axillary fossa (fossa axillaris /подмышечная ямка) is bounded:
- inferiorly by the pectoralis major in front and by the latissimus dorsi behind,
- medially by an imaginary line connecting the borders of these muscles on the chest,
- laterally by a line connecting these borders on the inner surface of the upper limb.
The axilllary cavity (cavum axillare /подмышечная полость) is bounded:
- The anterior wall is formed by the pectoralis major and pectoralis minor muscles.
- The posterior wall is formed by the latissimus dorsi, teres major and subscapular muscles.
- The medial wall is formed by the anterior serratus muscle.
- The lateral wall is formed by the humerus, coracobrachial and the short head of the biceps brachii.
· The axillar cavity ends in an opening inferiorly. Superiorly it narrows and communicates with the region of the neck. The cavity contains the vessels, nerves and lymph nodes.
· On the posterior wall of the axillary cavity is a triangular space formed by the surgical neck of the humerus laterally, the teres major muscle inferiorly and the subscapular muscle superiorly. This space is divided vertically by the long head of the triceps muscle into two openings:
- The lateral, quadrangular opening (foramen quadrilateraum /четырёхстороннее отверстие) is bounded by the surgical neck of the humerus laterally, the teres major muscle inferiorly, the subscapular muscle superiorly and the long head of the triceps muscle medially.
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- The medial, triangular opening (foramen trilaterum /трёхстороннее отверстие) is bounded by the teres major muscle inferiorly, the subscapular muscle superiorly and the long head of the triceps muscle laterally.
The radial canal (canalis nervi radialis /канал лучевого нерва) lies between the radial groove of the humerus anteriorly and the triceps muscle posteriorly. The canal has two openings:
- the superior opening (inlet) is between the upper and middle thirds of the arm on medial side. It is bounded by the humerus and the medial and lateral heads of the triceps muscle.
- the inferior opening (outlet) is between the middle and lower thirds of the arm on lateral side. It is bounded by the bracialis and bracioradialis muscles.
The lateral and medial bicipital grooves (sulcus bicipitalis lateralis, medialis /латеральная, медиальная борозда) are located on the anterior surface of the arm between the brachial muscle and the borders of the biceps brachii. The deeper, medial groove lodges the neurovascular bundle of the arm.
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