VERTEBRAL AND OCCIPITAL MUSCULATURE 339 



to the last rib, and is inserted on the lateral surfaces of the eight 

 posterior ribs. 



The splenius muscle is a somewhat triangular sheet arising 

 from the ligamentum nuchae and inserted on the supraoccipital 

 and mastoid portions of the skull, extending also to the transverse 

 process of the atlas. 



These two muscles should be divided, the serratus posterior 

 being removed from the surface. 



These and the muscles described in the next two sections con- 

 stitute the epaxial musculature (p. 67). 



1. The long muscles of the vertebral column. 



Apart from the iliopsoas, psoas minor, and quadratus lum- 

 borum — muscles of appendicular insertion lying on the ventral 

 surface of the vertebral column — the vertebral musculature com- 

 prises chiefly modified segmental muscles lying on the dorsal 

 surface, for the most part in the area enclosed by the spinous and 

 transverse processes of the vertebrae. They include the sacro- 

 spinalis, semispinalis, and intertransversarii. Their insertions are 

 extended in part laterad to the ribs. In the cervical region they 

 are represented by short muscles, separated for the most part from 

 the thoracic and lumbar portions, and arising by accessory bundles 

 from the anterior ribs, the corresponding thoracic, and the posterior 

 cervical vertebrae. In the cervical region the muscles are easily 

 separated from one another, but in the posterior part of the body 

 it is necessary to dissect away the tough investment of lumbo- 

 dorsal fascia which covers them. 



(a) The sacrospinalis. Origin: Crest of the ilium and dorsal 

 surface of the sacrum ; mamillary processes of the six pos- 

 terior lumbar vertebrae; investing lumbodorsal fascia. 



This muscle is the largest and strongest muscle of the 

 body. It extends forward over the surface of the ribs. Its 

 medial border is separated from the middle line by a space 

 of considerable width, in which the semispinalis and multi- 

 fidus muscles are accommodated. In the lumbar region it 

 is inserted in a continuous mass on the long transverse 

 processes of the vertebrae and in the interspaces. In the 

 thoracic region the muscle divides into two portions, name- 



