234 DORSAL MUSCLES OF THE TRUNK. 



ACTIONS. The serratus posticus superior elevates the upper ribs, and is therefore to 

 be regarded as a muscle of inspiration. The serratus inferior acts directly as a 

 depressor of the lower ribs, and may aid either in expiration or inspiration; in 

 expiration by acting in concert with the muscles which depress the higher ribs ; in 

 inspiration by fixing the lower ribs and giving firmness to the origin of the 

 diaphragm. 



SPLENITJS. The splenius muscle is so named from its having the form of 

 a strap, which binds down the parts lying under it. It is attached superiorly 

 in part to the cervical vertebrae, in part to the skull, and is described 

 accordingly under two names. 



a. The splenius colli is attached inferiorly to the spinous processes of the 

 third, fourth, fifth, and sixth dorsal vertebrae, and superiorly along with the 

 slips of the levator anguli scapulae to the transverse processes of the first two 

 or three cervical vertebrae. 



6. The splenius capitis, broader and thicker than the preceding, arises 

 from the spines of the seventh cervical and two upper dorsal vertebrae, and 

 from the ligamentum nuchae as high as the third cervical vertebrae. It is 

 inserted into the lower and back part of the mastoid process, and into the 

 outer part of the superior curved line of the occipital bone. 



The splenius is covered by the trapezius, the rhomboid, and the serratus posticus 

 superior ; and on the cranium by the sterno-mastoid. It conceals, in part, the 

 complexus and trachelo-mastoid. 



ERECTOR SPINJE. The erector spince may either Ve regarded as one large 

 composite muscle, or as consisting of seven distinct muscles. Viewed as 

 one muscle it may be conveniently considered as formed of three columns, 

 of which the inner, or that next the spine, is comparatively slender ; the 

 outer and inner columns of the remaining thicker mass consist each of a 

 large lower muscle and of two successive slender continuations in an upward 

 direction ; and to all these seven portions, or muscles, distinct names have 

 been given. 



The erector spinae takes origin inferiorly as a common mass, tlie outer 

 part of which is muscular, while the inner and larger part is tendinous. 

 The muscular portion arises from the posterior fifth of the crest of the ilium ; 

 the tendinous portion arises from the back part of the ilium, the lower and 

 back part of the sacrum, and the sacral and lumbar spines ; it is inseparably 

 united below with the lumbar aponeurosis, and is prolonged upwards on the 

 surface of the muscular part, concealing the multifidus spinae. The division 

 of the larger part into an external and internal column takes place below the 

 level of the last rib. 



a. The ilio-costalis (Theile) or sacro~lumbalis > the main muscle of the outer 

 column, is fleshy inferiorly, springing from that part of the common origin 

 which proceeds from the crest of the ilium ; it ends in a series of tendons 

 which incline slightly outwards, and are inserted one into each of the six or 

 seven lowest ribs at their angles. 



b. The musculus accessories ad ilio-costalem (ad sacro-lumbalem) is a con- 

 tinuation of the preceding muscle. It arises by flat tendons from the upper 

 margins of the lower six or eight ribs, internal to the tendons of the ilio- 

 costalis, and ends superiorly by continuing the series of those tendons to the 

 upper ribs. 



c. The cervicalis ascendens consists of slips in serial continuation with 

 those of the musculus accessorius, takiog origin from four or five of the 



