THE MUSCULAR SYSTEM. 141 



origin in the substance of this muscle, by union of two roots from 

 fifth and sixth cervical nerves. 



SCALENUS POSTICUS. Origin, from the outer surface of the 

 second rib, behind the serratus magnus; insertion, into the pos- 

 terior tubercles of the transverse processes of the lower two or 

 three cervical vertebrae; action, flexes and rotates the spine; 

 nerves, anterior branches of the lower cervical nerves. 



Of these muscles the scalenus medius is the longest and 

 largest, and the scalenus posticus the smallest. 



MUSCLES OF THE LARYNX AND EPIGLOTTIS (vide LARYNX). 



MUSCLES OF THE TRUNK. 



MUSCLES OF THE BACK. 



First Layer.. 



TRAPEZIUS. Origin, from inner third of superior curved 

 line of the occipital bone, the ligamentum nucliae, the spinous 

 processes of the seventh cervical, and all the dorsal vertebra; 

 insertion, into the outer third of the posterior border of the 

 clavicle, the inner margin of the acromion process, and the crest 

 of the spine of the scapula; action, draws the head backward; 

 nerves, cervical plexus and spinal accessory. 



LIGAMENTUM NUQH-.- Ongrw, from external* occipital 

 protuberance; insertion, spinous processes of the cervical verte- 

 brae, from the second to the seventh. This ligament is rudi- 

 mental in man, and in the lower animals sustains the head. 



LATISSIMUS DORSI. Origin, by an aponeurosis from the 

 spinous processes of the six lower dorsal, the lumbar and sacral 

 vertebrae, the supraspinous ligament, the crest of the ilium, and 

 the three or four lower ribs ; insertion, into the inner lip of the 

 bicipital groove of the humerus, in front of the teres major, and 

 a little above the pectoralis major; the tendon of this muscle 

 twists completely on itself, so that the superior fibres become the 

 inferior; action, draws the arm backward and downward, or, 

 fixing the arm, raises the lower ribs and draws the trunk forward ; 

 nerve, subscapular. 



Second Layer. 



LEVATOR ANGULI SCAPULAE. Origin, from three to five 

 tendons from the posterior tubercles of the transverse processes 

 of the three or five upper cervical vertebrae; insertion, into pos- 

 terior border of the scapula, at the root of the spine; action t 



