208 MUSCLES OF THE UPPER LIMB. 



The serratns magnus muscle, by withdrawing the scapula from the spinal column, 

 enables the arm when raised from the shoulder to be still farther outstretched, as in 

 the movement termed extension in fencing. It comes powerfully into action in all 

 movements of pushing; it likewise combines with the trapezius in rotating the 

 scapula. 



The latissimm dorsi carries the elevated arm downwards and backwards, rotating 

 it at the same time inwards, so as to make the palm look backwards, thus accomplish- 

 ing such a movement as is made by the arm in swimming. By passing over the 

 angle of the scapula it binds that process to the trunk, preventing its projection 

 backwards ; and by being folded round the outer border of the scapula, it limits the 

 projection outwards of the same angle when the arm is raised. 



The pectoralis major muscle, while it combines with the latissimus dorsi in 

 depressing the humerus from the raised position, opposes that muscle by drawing the 

 limb forwards. It is placed upon the stretch when the arms are thrown backwards, 

 and is most shortened when they are folded across the chest. 



Considered as acting on the trunk from the upper limb in a fixed condition, these 

 muscles have chiefly the following effect. They all tend to draw the trunk of the 

 body towards the limb, as in climbing, or other like efforts. The latissimus dorsi, if 

 acting on both sides, carries the body upwards and forwards, as in the use of crutches, 

 or in throwing a somersault from the hands backwards. The pectoral and latissimus 

 dorsi muscles are also muscles of forced inspiration, tending to raise and dilate the 

 ribs, more especially when the arms are elevated. The upper parts of both trapezii 

 muscles acting on the occipital bone aid the sterno-mastoid muscle in throwing for- 

 ward the chin ; and if one muscle only acts, it aids in rotating the head. 



MUSCLES OF THE SHOULDER. 



The deltoid is a coarsely fasciculated muscle, extending from the most 

 prominent part of the shoulder down a third of the upper arm. It arises 

 by a broad margin in three portions, an anterior from the external third of 

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

 from the lower border of the spine of the scapula as far back as the tri- 

 angular surface at the inner end of that portion of the bone, and the fasciculi 

 from the extended origin, converging as they descend, are inserted by a 

 comparatively narrow but thick extremity into the triangular rough surface 

 above the middle of the humerus, on its outer side. This rough surface 

 receives the name of the deltoid impression. 



At its posterior part the origin of the deltoid is thin and tendinous, and in the rest 

 of its extent fibrous septa dip down between the coarse muscular fasciculi. At the 

 insertion it is tendinous on the deep surface, and fibrous septa also project upwards 

 from thence into the substance of the muscle. The muscular fibres are arranged 

 pennately round those septa with such regularity as to have suggested to Albinus the 

 subdivision of the muscles into seven parts, four of- them broad above and narrow 

 below, and three intercalated between those parts, which are broad below and narrow 

 above. (Albinus, Histor. Muscul. Horn., p. 423.) 



At the posterior border of the deltoid, the aponeurosis covering the infraspinatus 

 muscle divides into two thin layers, of which one covers the muscle superficially, 

 and the other lines its deep surface. At its anterior border this muscle is in 

 contact with the pectoralis major, the cephalic vein lying between them. In 

 immediate contact with the deep surface is the large bursa, which separates this 

 muscle and the acromion from the shoulder joint and the muscles supporting it. 

 The deltoid muscle covers the origins of the biceps, coraco-brachialis, and long head of 

 the triceps, and the insertions of the subscapularis, supraspinatus, infraspinatus and 

 teres minor muscles, as also the circumflex vessels and nerve. 



The subscapularis muscle arises from all the venter of the scapula, with 

 the exception of the neck of the bone and the spaces occupied by the serratus 



