THE MUSCULAR SYSTEM. 143 



inferior angle upward and backward; nerves, branches of the 

 fifth cervical. 



Third Layer. 



SERRATUS POSTICUS SUPERIOR. Origin, from spinous proc- 

 esses of the two or three upper dorsal and last cervical vertebrae, 

 and from the ligarnentum nuchae; insertion, into upper borders 

 of the second to the fifth ribs inclusive; action, assists in respira- 

 tion; nerves, external branches of the posterior division of the 

 cervical. 



SERRATUS POSTICUS INFERIOR. Origin, from spinous proc- 

 esses and interspinous ligaments of two or three upper lumbar 

 and two lower dorsal vertebrae; insertion, into lower borders of 

 the four lower ribs, external to their angles ; action, elevates the 

 ribs ; assists in respiration ; nerves, external branches of the 

 posterior divisions of the lower dorsal. 



SPLENIUS. Origin, from spinous processes of last cervical 

 and six upper dorsal vertebrae, the lower half of the ligamentum 

 nuchae, and the supraspinous ligament; insertion, by two heads 

 splenius capitis into the occipital bone, just below the superior 

 curved line and the mastoid process of the temporal bone ; sple- 

 nius colli into posterior tubercles of the transverse processes of 

 the three or four upper cervical vertebrae; action, separately, 

 rotates the head and draws it to the other side; together, draw 

 the head backward; nerves, external branches of the posterior 

 divisions of the cervical. 



Fourth Layer. 



ERECTOR SriN^:. Origin, from sacro-iliac groove and from 

 a broad tendon attached internally to the spinous processes of 

 the lumbar and two or three lower dorsal vertebrae and supra- 

 spinous ligament; externally, the crest of the ilium and the 

 posterior part of the sacrum ; insertion, by two parts 1, sacro- 

 lumbalis (ilio-costalis), inserted into the angles of the six or 

 seven lower ribs; this muscle has two accessory portions, (a) 

 musculus accessorius ad sacro-lumbalem : origin, from angle of 

 six lower ribs; insertion, angles of six upper ribs; (b) cervical is 

 ascendens: uriyin, angles of the four or five upper ribs; inser- 

 tion,, into the posterior tubercles of the fourth to the sixth cer- 

 vical vertebra-, inclusive; 2, longissimus dorsi ; insertion, into 

 the transverse processes of all the dorsal vertebrae, and from the 

 seventh to the eleventh ribs, inclusive, bet \veen their angles ;m<l 

 tubercles; action, bends the trunk backward and erects the spine; 

 nerves, external branches of the posterior divisions of the lumbar 

 and dorsal, 



