THE MUSCLES AND FASCIAE OF THE UPPER LIMB. 



THE MUSCLES AND FASCIA OP THE SHOULDEK. 



FASCIJE. The deep fascia binds together the muscles of the shoulder with 

 considerable firmness, and over the back part of the deltoid and infraspinatus 

 muscles assumes a tendinous appearance. A strong and somewhat isolated portion, 

 bound down to the vertebral and axillary margins of the scapula, covers the infra- 

 spinatus and teres minor muscles as far as they are left uncovered by the deltoid. On 

 reaching the posterior border of the deltoid muscle, this aponeurosis divides into 

 two layers, of which the deeper is continued beneath the deltoid to the shoulder- 

 joint, and the more superficial forms the thin aponeurotic covering of that muscle, 

 becoming more and more slender as it passes forwards, and is attached to the lower 

 border of the spine. 



MUSCLES. The deltoid muscle is of a triangular form and coarsely fasciculated, 

 and extends from the most prominent part of the shoulder downwards for half the 

 length of the upper arm. It takes origin in an extended line which may be divided 

 into three portions, viz., an anterior from the front of the external third of the 

 clavicle, a middle from the point and outer edge of the acromion, and a posterior 

 from the lower border of the spine of the scapula as far back as the triangular sur- 

 face at its inner end. The fasciculi from these several parts converge as they 

 descend, and are inserted by a strong thick tendon into the deltoid eminence on the 

 outer side of the humerus. 



The three parts composing the deltoid muscle differ in the disposition of their muscular 

 fasciculi and tendons. The anterior and posterior portions are composed of parallel fasciculi 

 which, arising from the clavicle by short tendinous fibres, and by longer ones from the spine 

 of the scapula, are inserted into the outer surface of the marginal parts of the inferior tendon. 

 In the acromial portion, while some of the muscular fibres spring directly from the bone, yet 

 most of them arise in a pennif orm manner from the sides o.f tnree or. more frequently, four 

 tendinous septa, which pass downwards into the substance of the muscle. These oblique 

 fibres, running nearly parallel to each other, are inserted in a similar manner into the sides of 

 two or. more frequently, three septa which pass from below upwards and alternate with the 

 upper septa. The oblique fibres from the outside of the first and fourth upper septa are 

 inserted into the marginal parts of the main tendon. There are besides wedge-shaped bundles 

 of muscular fibres, arising directly from the acromion in the intervals between the penniform 

 bundles, which are inserted into the tips of the lower tendinous septa, and others which, 

 springing from the ends of the upper tendinous septa, are directly inserted into the humerus 

 between the lower septa. The main tendon of insertion spreads from below upwards for some 

 distance on the deep surface of the muscles. 



Relations. The anterior border of the deltoid is in contact with the pectoralis major 

 below, but separated from it by a small interval above : the cephalic vein, with a small 

 artery, lies between the two muscles. In contact with the deep surface is the large bursa 

 which separates this muscle and the acromion from the shoulder- joint an$ the muscles 

 supporting it. The deltoid muscle covers the origins of the biceps and coraco-brachialis. the- 

 insertions of the supraspinatus, infraspinatus and teres minor muscles, and parts of the long 

 and outer heads of the triceps, as well as the circumflex vessels and nerve. 



Varieties. The deltoid muscle is not subject to great varieties. One of the commonest 

 is a greater degree of subdivision of its parts than usual. Another is the continuation into it 

 of fibres from the trapezius, as in animals wanting the clavicle. Occasionally the anterior 

 part is closely united in its whole length with the great pectoral muscle. Additional slips 

 have been observed springing from the vertebral border of the scapula, from the infraspinous 

 fascia, and from the axillary border of the scapula, and joining the hinder part of the muscle,. 

 or expanding in the fascia covering it. Its insertion varies sometimes in extent. A remark- 

 able prolongation of its tendon on the radial border of the forearm, as far as the insertion of 

 the supinator longus, seems to repeat the tensor plicae alaris of the bird (Macalister). 



The supraspinatus muscle arises from the supraspinous fossa of the scapula 

 to within a short distance of the neck of the bone, and from an aponeurosis by 

 which it is covered. Its fibres converge beneath the acromion to a tendon, which 

 adheres to the capsule of the shoulder-joint and to the tendon of the infraspinatus- 



