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THE MUSCLES AND FASCIA OF THE SHOULDER 439 



the chest. It arises by fleshy digitations from the outer surfaces and superior 

 borders of the upper eight or nine ribs, and from the aponeuroses covering the 

 intervening Intercostales. Each digitation (except the first) arises from the 

 corresponding rib ; the first springs from the first and second ribs ; and from the fascia 

 covering the first intercostal space. From this extensive attachment the fibers 

 pass backward, closely applied to the chest-wall, and reach the vertebral border 

 of the scapula, and are inserted into its ventral surface in the following manner, 

 he first digitation is inserted into a triangular area on the ventral surface of the 

 edial angle. The next two digitations spread out to form a thin, triangular 

 sheet, the base of which is directed backward and is inserted into nearly the whole 

 length of the ventral surface of the vertebral border. The lo\ver five or six digita- 

 tions converge to form a fan-shaped mass, the apex of which is inserted, by muscular 

 and tendinous fibers, into a triangular impression on the ventral surface of the 

 inferior angle. The lo\ver four slips interdigitate at their origins with the upper 

 five slips of the Obliquus externus abdominis. 



Variations. Attachment to tenth rib. Absence of attachments to first rib, to one or more of 

 he lower ribs. Division into three parts; absence or defect of middle part. Union with Levator 

 scapulae, External intercostals or External oblique. 



Nerves. The Pectoralis major is supplied by the medial and lateral anterior thoracic nerves; 

 through these nerves the muscle receives filaments from all the spinal nerves entering into the 

 formation of the brachial plexus; the Pectoralis minor receives its fibers from the eighth cervical 

 and first thoracic nerves through the medial anterior thoracic nerve. The Subclavius is suplied 

 by a filamen-t from the fifth and sixth cervical nerves; the Serratus anterior is supplied by the 

 long thoracic, which is derived from the fifth, sixth, and seventh cervical nerves. 



Actions. If the arm has been raised by the Deltoideus, the Pectoralis major will, conjointly 

 with the Latissimus dorsi and Teres major, depress it to the side of the chest. If acting alone, 

 it adducts and draws forward the arm, bringing it across the front of the chest, and at the same 

 time rotates it inward. The Pectoralis minor depresses the point of the shoulder, drawing the 

 scapula downward and medialward toward the thorax, and throwing the inferior angle back- 

 ward. The Subclavius depresses the shoulder, carrying it downward and forward. When the 

 arms are fixed, all three of these muscles act upon the ribs; drawing them upward and expand- 

 ing the chest, and thus becoming very important agents in forced inspiration. The Serratus 

 anterior, 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 fibers 

 move forward the lower angle and assist the Trapezius in rotating the bone at the sternoclavicular 

 joint, and thus assist this muscle in raising the acromion and supporting w r eights upon the shoulder. 

 It is also an assistant to the Deltoideus in raising the arm, inasmuch as during the action of this 

 latter muscle it fixes the scapula and so steadies the glenoid cavity on which the head of the 

 humerus rotates. After the Deltoideus has raised the arm to a right angle with the trunk, the 

 "Serratus anterior and the Trapezius, by rotating the scapula, raise the arm into an almost vertical 

 position. It is possible that when the shoulders are fixed the lower fibers of the Serratus anterior 

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

 formerly believed to be 



IE. THE MUSCLES AND FASCLffi OF THE SHOULDER. 



In this group are included: 



Deltoideus. Infraspinatus. 



Subscapularis. Teres minor. 



Supraspinatus. Teres major. 



Deep Fascia. The deep fascia covering the Deltoideus invests the muscle, and 

 sends numerous septa between its fasciculi. In front it is continuous with the fascia 

 covering the Pectoralis major; behind, where it is thick and strong, with that 

 covering the Infraspinatus; above, it is attached to the clavicle, the acromion, 

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

 arm. 



The Deltoideus (Deltoid muscle) (Fig. 410) is a large, thick, triangular muscle, which 

 covers the shoulder-joint in front, behind, and laterally. It arises from the anterior 



