THE TRUNK MUSCLES. • 513 



verse or articulating processes of all the vertebrae as far up as the fourth cervical. 

 The fibres from each vertebra pass over from two to four of the succeeding vertebrae 

 and are inserted into the spinous processes of the third to the fifth, the entire insertion 

 of the muscle extending from the spinous process of the last lumbar vertebra to that 

 of the axis. 



Nerve-Supply. — From the posterior divisions of the spinal nerves from the 

 third cervical to the last lumbar. 



Action. — To bend the spinal column backward and rotate it towards the op- 

 posite side. 



4. RoTATORES (Fig. 521). 



Attachments. — The rotatores {rotatores dorsi) form the deepest layer of the 

 muscles occupying the spino-transverse groove. They form a series of small muscles 

 hardly distinguishable from the bundles of tlje multifidus, beneath which they lie. 

 They are to be found along the entire length of the spinal column from the sacrum to 

 the axis, arismg from the transverse process of one vertebra and passing, some of the 

 fibres to the base of the spinous process of the rtext succeeding vertebra {rotatores 

 breves) and the rest to a corresponding point of the second vertebra above {rotatores 

 longj). 



Nerve-Supply. — From the posterior divisions of the spinal nerves from the 

 third cervical to the last lumbar. 



Action. — To bend the spinal column backward and rotate it towards the op- 

 posite side. 



5. Interspinales (Fig. 521). 



Attachments. — The interspinales are relatively small muscles which pass be- 

 tween tiie spinous processes of succeeding vertebrae. They are usually absent 

 throughout the greater portion of the thoracic region, occurring only in connection 

 with the first and the last two spines, but they are exceptionally well developed in 

 the lumbar region and are usually paired in the cervical region, where they stop at 

 the axis. 



Nerve-Supply. — From the posterior divisions of the spinal nerves from the 

 third cervical to the fifth lumbar. 



Action. — Acting together to bend the cervical and lumbar portions of the spinal 

 column backward. 



6. Intertransversales (Fig. 521). 



Attachments. — The name intertransversales (mm. intertransversarii) has been 

 • applied to a series of small muscles occurring in the cervical and lumbar regions and 

 extending between the transverse or mammillary processes of successive vertebrae. 

 In each of the regions named two sets of intertransversales are recognized, but it 

 seems probable that only one of the sets in such region belongs to the dorsal group 

 of muscles. This set will alone be considered here, the other (anterior) one being 

 described with the ventral muscles of the regions in which it occurs. 



The intertransversarii posteriores occur only in the cervical region and extend 

 between the posterior tubercles of the transverse processes of succeeding vertebrae. 

 The intertransversarii mediales occur only in the lumbar region and extend between 

 the mammillary processes of successive vertebrae. 



Nerve -Supply. — Probably by fibres belonging to the posterior divisions of the 

 cervical and lumbar nerves, but it is at present insufficiently determined. 



Action. — To bend the cervical and lumbar portions of the vertebral column 

 laterally. 



7. Rectus Capitis Posticus Major (Fig. 522). 



Attachments. — The greater straight muscle (m. rectus capitis posterior major) 

 arises from the apex of the spinous process of the axis and passes upward and out- 

 ward, broadening as it goes, to be inserted into the middle portion of the inferioi 

 nuchal line, 



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