382 THE MU8CLEK AXJ) FAMINE. 



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

 behind, by the Subscapularis. The axillary vessels and nerves lie upon its upper 

 part, while its deep surface rests upon the ribs and intercostal muscles. 



Nerve. The Serratus magnus is supplied by the posterior thoracic nerve, which 

 is derived from the fifth, sixth, and generally the seventh cervical nerves. 



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 also an assistant to the Deltoid in raising the arm, inasmuch as 

 during the action of this latter muscle it fixes the scapula and so steadies the glen- 

 oid cavity on which the head of the humerus rotates. After the Deltoid has raised 

 the arm to a right angle with the trunk, the Serratus magnus and the Trapezius, 

 by rotating the scapula, raise the arm into an almost vertical position. It is pos- 

 sible that when the shoulders are fixed the lower fibres of the Serratus magnus may 

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

 cle which it was formerly believed to be. 



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

 the lower angle of the scapula, leaves the ribs and stands out prominently on the surface, giving 

 a peculiar "winged" appearance to the back. The patient is unable to raise the arm, and an 

 attempt to do so is followed by a further projection of the lower angle of the scapula from the 

 back of the thorax. 



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. 228, No. 3). 



II. MUSCLES AND FASCLS1 OF THE SHOULDER AND ARM 



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. 



3. 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. 229) 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 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 



