THE MUSCULAR SYSTEM 



2«I 



thoracic cavity is enlarged. The curvature of the diaphragm is restored 

 when the intercostal muscles relax and the abdominal muscles push the 

 viscera against the diaphragm. 



Shoulder and Chest Muscles. The muscles of the shoulder and chest 

 function chiefly in relation to the arms. The most superficial of these 

 on the back is the trapezius which elevates the shoulder and in conjunction 

 with the rhomboideus draws the shoulder blade towards the backbone. 

 Underneath the trapezius, the rhomboideus major and minor also draw 

 the shoulder blade towards the backbone. The deltoideus is the shield- 

 shaped muscle which covers the shoulder and extends from the scapula to 



M. TRANSVERSOSPINALIS. 

 TRANSVERSE PROCESS. 

 M QUADRATUS 

 LUMBORLM 



,-M LDNGISSIMUS OORSI. 



M RHOMBOIDEUS. 



•M. SERRATUS POSTERIOR. 

 ^SCAPULA. 



M. LATISSIMUS DORSI. 

 GLENOID CAVITY. 



M. EXTER^4AL 

 OBLIQUE. 

 M. RECTUS ABDOMINIS^ 



'ACROMION. 

 tORACDID. 

 -■M. SUBCLAVIUS. 



M. BRACHIALIS' 

 PECTORALIS MAJOR. INFERIOR. 



M. TRANSVERSUS THORACIS. 



MANLBRIUM STERNi; 



CLAVICLE-; 



Fig. 234. — Thoracic and lumbar muscles of man as seen in cross section. Thoracic 

 muscles on the right, lumbar on the left. (Redrawn after Braus.) 



the humerus. Its chief function is to abduct the arm. The supra- 

 spinatus and infraspinatus muscles on the dorsal side of the scapula 

 together with the teres minor help to rotate the arm. On the under 

 surface of the scapula the subscapularis is an inward rotator. The teres 

 major muscle adducts the arm towards the body. The latissimus dorsi 

 is a broad muscle, inserted on the humerus, which draws the arm down 

 and backward. In the region of the chest, the pectoralis major and minor 

 are the chief muscles. They adduct the arm. The subclavius is a small 

 muscle connecting the clavicle with the first rib, used in depressing the 

 clavicle. The serratus anterior extends from the scapula to the first nine 

 ribs and draws the shoulder forward. 



Muscles of the Upper Arm. The intrinsic rnuscles of the arm are 

 divided into dorsal or extensor muscles and ventral or flexor muscles. 

 Included in the dorsal group are the triceps and anconeus which extend 

 the forearm. The biceps, coraco-brachialis, brachiaUs constitute the 

 ventral group. The coraco-brachialis flexes the arm, the biceps and 



