FUNCTIONS OF MUSCLES 503 



10. Muscles of respiration. 



Quiet inspiration: the external intercostals, intercartilaginous parts of internal 

 intercostals, diaphragm. 



Enforced inspiration: in addition to the muscles mentioned above, the scaleni, 

 sterno-cleido-mastoid, serratus posterior superior and inferior, 

 rhomboids, .serratus anterior, latissimus dorsi, subclavius, 

 pectoralis major and minor, and- 4he -extensors .of the spinal 

 cuLuiQii, the trapezius and the levator scapuU. 



Quiet expiration: interosseous parts of internal intercostals, subcostales, and 

 transversus thoracis. 



Enforced expiration: in addition to the muscles mentioned above, the abdominal 

 muscles, ilio-costahs lumborum and dorsi, longissimus dorsi, 

 and the quadratus lumborum. 



The chief muscles of respiration are the intercostals; the diaphragm plays a minor 

 part (Fick). 



11. Muscles acting on the abdomen. 



(a) Constriction of the abdominal cavity: obliquus abdominis externus and 



internus, the transversus and rectus abdominis, and the dia- 

 phragm, levator ani, and coccj'geus. 



(b) Reduction of presssure in the abdominal cavity: the muscles of inspiration, 



with the exception of the diaplu-agm, serve to lessen the com- 

 pression of the abdominal viscera. 



12. Action of the muscles of the perineal region. 



(a) To close anal canal: sphincter ani externus. 



(6) To constrict the anal portion of the rectum: levator ani (pubo-coccygeal 

 portion). 



(c) To constrict the bulbus urethra and the corpus cavernosum urethrae (corpus 



spongiosum): bulbo-cavernosus. 



(d) To elevate the prostate gland: levator ani. 



(e) To constrict the vagina: bulbo-cavernosus, levator ani (pubo-coccygeal por- 



tion), constrictor vaginae. 



(/) To cause erection of penis and chtoris: ischio-caveruosus, bulbo-cavernosus, 

 and sphincter urethrae membranaceae. 



(g) To compress the urethra and the bulbo-urethral (Cowper's) or the great ves- 

 tibular (Barthohn's) gland: sphincter urethrae membranacea? 

 and the transversus perinei profundus. 



(h) To support and hft the pelvic floor : levator ani, coccygeus, transversus perinei 

 profundus and superficialis. 



13. Muscles acting on the shoulder-girdle. 



The two joints acted upon are the sterno-clavicular and the acromio-clayicular. 

 The movements produced consist in lifting and lowering the 

 scapula, carrying it forward and backward and rotating it. 



(a) Elevation: trapezius (upper portion), levator scapulae, sterno-cleido-mastoid, 



rhomboidei, pectorahs major (upper sternal part), serratus 

 anterior (middle portion], omo-hyoid. 

 (6) Depression: trapezius (lower portion), pectoralis major (lower portion), 

 pectoralis minor, subclavius. latissimus dorsi, serratus anterior 

 (lower part). The weight of the limb is likewise a factor. 



(c) Forward movement: serratus anterior, pectorales major and minor. 



(d) Backward movement: trapezius, rhomboidei, latissimus dorsi. 



(e) Rotation: 



Associated with abduction of the arm: serratus anteriorT (inferior 



portion), trapezius. 

 Associated with adduction of the arm: rhomboidei, pectoralis major 



(pectoral portion), latissimus dorsi, pectoralis minor, levator 



scapulae. 



14. Muscles acting on the arm at the shoulder-joint. 



(o) To flex it, 



WTien the arm is at the side: pectoralis major (upper part), deltoid (anterior 



part), short head of biceps, coracobrachialis, infraspinatus, 



long head of biceps, teres minor, subscapularis (upper part), 



supraspinatus. 

 When the arm is abducted 60°: pectoralis major, deltoid, subscapularis, 



short head of biceps, coracobrachialis, long head of biceps, 



infraspinatus, supraspinatus. 

 The movement is aided by the trapezius and the serratus anterior. 



(b) To extend it. 



WTien the arm is at the side: latissimus dorsi, deltoid (posterior part), teres 

 major, subscapularis (lower part), triceps. 



WTien the arm is abducted 60°: latissimus dorsi, deltoid, teres major, triceps, 

 teres minor. 



The upper and middle portions of the trapezius and the levator scapulae play 

 an important part in extension of the arm. 



(c) To abduct it. 



\Yhen the arm is at the side: deltoid, supraspinatus, long head of biceps, 

 subscapularis, infraspinatus (upper part). 



When the arm is abducted 60°: deltoid, supraspinatus, infraspinatus (upper 

 part), long head of biceps, short head of biceps. 



