ACROMIAL AND SCAPULAR REGIONS. 209 



ACROMIAL KEGION. 

 Deltoid. 



The deep fascia covering the Deltoid (deltoid aponeurosis) is a thick and strong 

 fibrous layer, which covers the outer surface of the muscle, and sends down nume- 

 rous prolongations between its fasciculi ; it is continuous, internally, with the 

 fascia covering the great Pectoral muscle ; behind, with that covering the Infra- 

 spinatus and back of the arm ; above, it is attached to the clavicle, the acromion, 

 and spine of the scapula. 



The Deltoid is a large, thick, triangular muscle, which forms the convexity of 

 the shoulder, and has received its name from its resemblance to the Greek letter A 

 reversed. It surrounds the shoulder-joint in the greater part of its extent, 

 covering it on its outer side, and in front and behind. It arises from 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 whole length of 

 the lower border of the spine of the scapula. From this extensive origin, the 

 fibres converge towards their insertion, the middle passing vertically, the anterior 

 obliquely backwards, the posterior obliquely forwards ; 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. This muscle is remarkably coarse in texture, and 

 intersected by three or four tendinous lamina ; these are attached, at intervals, to 

 the clavicle and acromion, extend into the substance of the muscle, and give origin 

 to a number of fleshy fibres. The largest of these laminae extends from the 

 summit of the acromion. 



Relations. By its superficial surface, with the Platysma, supra-acromial nerves, 

 the superficial fascia, and integument. 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, tendon of the Pectoralis major, Teres minor, scapular and external 

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

 anterior border is separated from the Pectoralis major by a cellular interspace, 

 which lodges the cephalic vein and descending branch of the acromial-thoracic 

 artery. Its posterior border rests on the Infra-spinatus 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 forwards; and its posterior fibres, aided by the Teres major and 

 Latissimus dorsi, draw it backwards. 



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 downwards ; 

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

 insertion of the muscle should be carefully examined. 



ANTERIOR SCAPULAR KEGION. 

 Subscapularis. 



The sul)sca%)ular aponeurosis is a thin membrane, attached to the entire circum- 

 ference 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 latter 

 is exposed. 



The Subscapularis 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 inner side of the superior and inferior angles, 

 which afford attachment to the Serratus magnus. Some fibres arise from tendinous 

 laminae, which intersect the muscle, and are attached to ridges on the bone ; and 

 others from an aponeurosis, which separates the muscle from the Teres major and 



