470 



THE MUSCLES AND FASCIA. 



Nerves.- 



Slip of SERRATUS MAGNUS to 1st rib. 



Spine of scapula. 



fleshy fibres proceed obliquely upward and outward, to be inserted into a deep 

 groove on the under surface of the middle third of the clavicle. 



Relations. By its upper surface, with the clavicle. By its under surface it is 

 separated from the first rib by the subclavian vessels and brachial plexus of nerves. 

 Its anterior surface is separated from the Pectoralis major by the costo-coracoid 

 membrane, which, with the clavicle, forms an osseo-fibrous sheath in which the 

 muscle is enclosed. 



If the costal attachment of the Pectoralis minor is divided across, and the muscle reflected 

 outward, the axillary vessels and nerves are brought fully into view, and should be examined. 



The Pectoral muscles are supplied by the anterior thoracic nerves ; 

 the Subclavius, by a filament from the cord 

 formed by the union of the fifth and sixth 

 cervical nerves. 



Actions. If the arm has been raised by 

 the Deltoid, the Pectoralis major will, con- 

 jointly with the Latissimus dorsi and Teres 

 major, depress it to the side of the chest. 

 If acting alone, it adducts and draws for- 

 ward 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 inward to the thorax, and 

 throwing the inferior angle backward. The 

 Subclavius depresses the shoulder, drawing 

 the clavicle downward and forward. When 

 the arms are fixed, all three muscles act upon 

 the ribs, drawing them upward and expand- 

 ing the chest, and thus becoming very 

 important agents in forced inspiration. 

 Asthmatic patients always assume an atti- 

 tude which fixes the shoulders, so that all 

 these muscles may be brought into action to 

 assist in dilating the cavity of the chest. 



Lateral Thoracic Region. 



Serratus magnus. 



The Serratus magnus (Fig. 304) is a 

 broad, thin, and irregularly quadrilateral 

 muscle, situated at the upper part and 

 side of the chest. It consists of two tri- 

 angular or fan-shaped portions ; the upper 

 one having the apex of the triangle at- 

 FIG. 304 -Serratus magnus. (From a prep- tached to the first and second ribs, and the 



aration in the Museum of the Royal College of i , , -, j . t i i_ j 



Surgeons of England.) base to the upper angle and vertebral border 



of the scapula ; the lower with its apex 



behind attached to the inferior angle of the scapula, and its base in front con- 

 nected with the ribs from the second to the eighth. It arises by nine fleshy 

 digitations from the outer surface and upper border of the eight upper ribs (the 

 second rib having two), and from the aponeurosis covering the upper intercostal 

 muscles, and is inserted into the whole length of the anterior aspect of the poste- 

 rior border of the scapula. The upper fan-shaped portion is attached to the fore 

 part of the outer surfaces of the first and second ribs ; its fibres spread out, the 

 upper ones forming a thick fasciculus, which passes upward and backward, and 

 is attached to the triangular smooth surface on the anterior aspect of the superior 

 angle of the scapula ; the remaining fibres proceed backward and downward to 



IEXTKHNU* OBLIQUUS. 



8th rib. 



