RESPIRA TIOX. 405 



trapezius passes from the occipital bone, the ligamentum nucha?, the spines of 

 the seventh cervical and of all the dorsal vertebra, and the supraspinous liga- 

 ment to the posterior border of the outer third of the clavicle, the inner border 

 of the acromion process, the crest of the spine of the scapula, and to the 

 tubercle near the root. The trapezei help to fix the shoulders. The rhomboid- 

 eus minor passes from the ligamentum nucha? and the spines of the seventh 

 cervical and first dorsal vertebrae to the root of the spine of the scapula. The 

 rhomboideus major passes from the spines of the first four or five dorsal vertebrae 

 and the supraspinous ligament to the inferior angle of the scapula. The trapezei 

 and rhomboidei fix the shoulders, affording a base of action from which the 

 pectorales act. The pectoralis major passes from the pectoral ridge of the 

 humerus to the inner half of the anterior surface of the clavicle, the corre- 

 sponding half of the anterior surface of the sternum, the cartilages of the 

 first six ribs, and the aponeurosis of the external oblique muscle. The pecto- 

 ralis minor passes from the coracoid process of the scapula to the upper margin 

 and outer surface of the third, fourth, and fifth ribs close to the cartilages and 

 to the intercostal aponeuroses. The pectorales minores and the costal portion 

 of the pectorales majores raise the ribs when the shoulders are fixed. The 

 erectorcs spina? are composite muscles extending along each side of the spinal 

 column, each consisting of the sacro-lumbalis, the musculus accessorius, the 

 cervicalis ascendens, the longissimus dorsi, the transversalis cervicis, the trachelo- 

 mastoid, and the spinalis dorsi. The erectores spinae straighten and extend the 

 spine and the neck, and thus tend to raise the sternum, the costal cartilages, 

 and the ribs. The infrahyoidei may also be included among the muscles 

 engaged in forced inspiration, since they may aid in the elevation of the sternum. 



Summary of the Actions of the Chief Muscles of Inspiration. — Dur- 

 ing quiet inspiration the diaphragm contracts, thus increasing the vertical diam- 

 eter of the thorax, its effectiveness being augmented by the associated actions 

 of the quadrati lumborum and the serrati postici inferiores, the tinnier fixing 

 the twelfth ribs, and the latter fixing the ninth, tenth, eleventh, and twelfth 

 ribs, and thus preventing the muscular slips of the diaphragm attached to these 

 ribs from drawing them inward and upward and thus diminishing the cavity 

 of the thorax. Coincidcntly with the contractions of these muscles the seal ni 

 fix the first and second ribs, and the serraU postici superiores aid in fixing the 

 second ribs and elevate the third, fourth, and fifth ribs ; the intercostales extemi 

 et intercartilaghiei and the levatores costarum tongi > I bn ves elevate and evert the 

 first to the tenth ribs, inclusive, throwing the lower end of the sternum for- 

 ward; and the levatorcs, in conjunction with the quadrati lumborum and the 

 8t ■rrati postici inferiores, aid in fixing the lower ribs and even draw them buck- 

 ward. The intercostales extern/ also serve to maintain a proper degree of tension 

 of the intercostal tissues. 



During forced inspiration the scaieni and the serrati postici superiores act 

 more powerfully and thus raise the sternum with its attached costal cartilages 

 and ribs, being assisted by the sterno-cleido-Tnastoidei and the infrahyoidei 

 when the head and neck are fixed, and by the pectorales majores et minores 



