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.

• 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.