THE ACRO^fIAL REGION. 471 



be attached to the posterior border of the scapula between the superior and inferior 

 angles. The lower fan-shaped portion is attached posteriorly by its apex to the 

 anterior surface of the inferior angle of the scapula, partly by muscular, partly 

 bv tendinous fibres ; it spreads out like a fan, the upper fibres passing forward 

 and upward, the lower horizontally forward to be inserted into the outer surface 

 of the fore part of the ribs from the second to the eighth, by a series of muscular 

 digitations. In the intervals between the four lower of these are received cor- 

 responding processes of the External oblique. 



Relations. This muscle is covered, in front, by the Pectoral muscle ; behind 

 by the Snbscapularis ; above, by the axillary vessels and nerves. Its deep surface 

 rests upon the ribs and Intercostal muscles. 



Nerves. The Serratus rnagnus is supplied by the posterior thoracic nerve. 



Actions. The Serratus magnus, as a whole, carries the scapula forward, and 

 at the same time raises the vertebral border of the bone. It is therefore concerned 

 in the action of pushing. Its lower and stronger fibres move forward the lower 

 angle and assist the Trapezius in rotating the bone round an axis through its centre, 

 and thus assists this muscle in raising the acromion and supporting weights upon 

 the shoulder. It is possible that when the shoulders are fixed the lower fibres 

 may assist in raising and everting the ribs ; but it is not the important inspiratory 

 muscle which it was formerly believed to be. 



Surgical Anatomy. -When the muscle is paralyzed the vertebral border, and especially 

 the lower angle, leave the ribs and stand out prominently on the surface, giving a peculiar 

 "winged appearance to the back. The patient is unable to raise the arm above a right angle, 

 and an attempt to do so is followed by a revolution of the scapula, instead of by the elevation 

 of the arm. 



Dissection. After completing the dissection of the axilla, if the muscles of the back have 

 been dissected, the upper extremity should be separated from the trunk. Saw through the 

 clavicle at its centre, and then cut through the muscles which connect the scapula and arm with 

 the trunk, viz. : the Pectoralis minor in front, Serratus magnus at the side, and the Levator 

 anguli scapulae, the Rhomboids. Trapezius. and Latissimus dorsi behind. These muscles should 

 be cleaned and traced to their respective insertions. Then make an incision through the integu- 

 ment, commencing at the outer third of the clavicle, and extending along the margin of that 

 bone, the acromion process, and spine of the scapula ; the integument should be dissected from 

 above downward and outward, when the fascia covering the Deltoid is exposed (Fig. 301, No. 3). 



The superficial fascia of the upper extremity is a thin cellulo-fibrous layer, 

 containing the superficial veins and lymphatics, and the cutaneous nerves. It is 

 most distinct in front of the elbow, and contains very large superficial veins and 

 nerves : in the hand it is hardly demonstrable, the integument being closely 

 adherent to the deep fascia by dense fibrous bands. Small subcutaneous bursae are 

 found in this fascia over the acromion, the olecranon, 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 considered in the description of the muscles of 

 the several regions. 



Acromial Region. 

 Deltoid. 



The deep fascia covering the Deltoid (deltoid aponeurosis) is a fibrous layer 

 which covers the outer surface of the muscle, thick and strong behind, where it 

 is continuous with the infraspinatus fascia, thinner over the rest of its extent. 

 It sends down numerous prolongations between the fasciculi of the muscle. 

 In front, it is continuous with the fascia covering the great Pectoral muscle ; 

 behind, with that covering the Infraspinatus ; above, it is attached to the clavicle, 

 the acromion, and spine of the scapula ; below, it is continuous with the deep fascia 

 of the arm. 



The Deltoid (Fig. 302) is a large, thick, triangular muscle, which gives the 

 rounded outline to the shoulder, and has received its name from its resemblance to 

 the Greek letter /\ 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 



