472 THE MUSCLES AND FASCIA 



the outer third of the anterior border and upper surface of the clavicle ; from the 

 outer margin and upper surface of the acromion process, and from the lower lip of 

 the posterior border of the spine of the scapula, as far back as the triangular 

 surface at its inner end. From this extensive origin the fibres converge toward 

 their insertion, the middle passing vertically, the anterior obliquely backward, the 

 posterior obliquely forward ; they unite to form a thick tendon, which is inserted 

 into a rough prominence on the middle of the outer side of the shaft of the 

 humerus. At its insertion the muscle gives off an expansion to the deep fascia of 

 the arm. This muscle is remarkably coarse in texture, and the arrangement of 

 its muscular fibres is somewhat peculiar ; the central portion of the muscle that 

 is to say, the part arising from the acromion process consists of oblique fibres, 

 which arise in a bipenniform manner from the sides of tendinous intersections, 

 generally four in number, which are attached above to the acromion process and 

 pass downward parallel to one another in the substance of the muscle. The 

 oblique muscular fibres thus formed are inserted into similar tendinous intersec- 

 tions, generally three in number, which pass upward from the insertion of the 

 muscle into the humerus and alternate with the descending septa. The lateral 

 portions of the muscle that is to say, the fibres arising from the clavicle and 

 spine of the scapula are not arranged in this manner, but consist of parallel 

 fasciculi passing from their origin above, to be inserted into the margins of the 

 inferior tendon. 



Relations. By its superficial surface, with the integument, the superficial 

 fascia, Platysma, and supra-acromial nerves. Its deep surface is separated from 

 the head of the humerus by a large sacculated synovial bursa, and covers the 

 coracoid process, coraco-acromial ligament, Pectoralis minor, Coraco-brachialis, 

 both heads of the Biceps, the tendon of the Pectoralis major, the insertions 

 of the Supraspinatus, Infraspinatus, and Teres minor, the scapular and 

 external heads of the Triceps, the circumflex vessels and nerve, and the humerus. 

 Its anterior border is separated at its upper part from the Pectoralis major by 

 a cellular interspace, which lodges the cephalic vein and descending branch of the 

 acromial thoracic artery : lower down the two muscles are in close contact. Its 

 posterior border rests on the Infraspinatus and Triceps muscles 

 Nerves. The Deltoid is supplied by the circumflex nerve- 

 Actions. The Deltoid raises the arm directly from the side, so as to bring it 

 at right angles with the trunk. Its anterior fibres, assisted by the Pectoralis 

 major, draw the arm forward; and its posterior fibres, aided by the Teres major 

 and Latissimus dorsi, draw it backward. 



Surgical Anatomy. The Deltoid is very liable to atrophy, and when in this condition 

 simulates dislocation of the shoulder-joint, as there is flattening of the shoulder and apparent 

 prominence of the acromion process ; upon examination, however, it will be found that the 

 relative position of the great tuberosity of the humerus to the acromion and coracoid process is 

 unchanged. Atrophy of the Deltoid may be due to disuse or loss of trophic influence, either 

 from injury to the circumflex nerve or cord lesions, as in infantile paralysis. 



Dissection. Divide the Deltoid across, near its upper part, by an incision carried along the 

 margin of the clavicle, the acromion process, and spine of the scapula, and reflect it downward : 

 the bursa will be seen on its under surface, as well as the circumflex vessels and nerve. 



Anterior Scapular Region. 



Subscapularis. 



The subscapular fascia is a thin membrane attached to the entire circumference 

 of the subscapular fossa, and affording attachment by its inner surface to some of 

 the fibres of the Subscapularis muscle : when this is removed, the Subscapularis 

 muscle is exposed. 



The Subscapularis (Fig. 303) is a large triangular muscle which fills up the 

 subscapular fossa, arising from its internal two-thirds, with the exception of a 

 narrow margin along the posterior border, and the surfaces at the superior and 

 inferior angles which afford attachment to the Serratus magnus. Some fibres 



