ACROMIAL AND SCAPULAR REGIONS. 377 



integument being closely adherent to the deep fascia by dense fibrous bands. 

 Small subcutaneous bursae are found in this fascia, over the acromion, the ole- 

 cranon, and the knuckles. The deep fascia of the upper extremity comprises 

 the aponeurosis of the shoulder, arm, and forearm, the anterior and posterior 

 annular ligaments of the carpus, and the palmar fascia. These will be con- 

 sidered in the description of the muscles of the several regions. 



ACROMIAL REGION. 

 Deltoid. 



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

 strong fibrous layer, which incloses the outer surface of the muscle, and sends 

 down numerous prolongations between its fasciculi ; it is continuous, internally, 

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

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

 the acromion, and spine of the scapula. 



The Deltoid (Fig. 236) 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 laminae; 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, Triceps 

 (its scapular and external heads), the circumflex vessels and nerve, and the 

 humerus. Its anterior border is separated from the Pectoralis Major by a cellu- 

 lar interspace, which lodges the cephalic vein and descending branch of the 

 thoracico-acromialis artery. 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 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 nerve. The 

 insertion of the muscle should be carefully examined. 



ANTERIOR SCAPULAR REGION. 

 Subscapularis. 



The subscapular aponeurosis is a thin membrane, attached to the entire cir- 

 cumference 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. 



