72 HEAD AND NECK 



Musculus Semispinalis. The semispinalis dorsi is composed of a 

 series of muscular slips, with long tendons at each end, which arise from 

 the transverse processes of the sixth to the tenth thoracic vertebrae. It is 

 inserted into the spines of the upper four thoracic and lower two cervical 

 vertebrae. The semispinalis cervicis lies under cover of the semispinalis 

 capitis. It springs from the transverse processes of the upper five thoracic 

 vertebrae, and is inserted into the spines of the second to the fifth cervical 

 vertebras. The slips composing the semispinalis muscles stretch over five 

 or more vertebrae. The fibres of the semispinalis run upwards and medi- 

 ally. Therefore they turn the trunk and neck to the opposite side. They 

 are supplied by the posterior rami of the spinal nerves. 



Dissection. The fourth layer of muscles must now be 

 examined. It includes the multifidus, the rotatores, the inter- 

 spinales, the intertransversales, and the recti and oblique muscles 

 of the sub-occipital region. The latter have already been exposed 

 by the reflection of the splenius and semispinalis capitis (corn- 

 plexus). To display the other members of the group the semi- 

 spinalis dorsi and cervicis must be detached from the spines and 

 drawn aside, and the sacrospinalis must be separated from the 

 lumbar and sacral spines and turned laterally, if that has not 

 already been done in tracing the nerves. 



Musculus Multifidus. In the lumbar and sacral regions the multi- 

 fidus will be seen to constitute a thick fleshy mass which clings closely 

 to the vertebral spines. In that situation it has a very extensive origin 

 viz., (i) from the deep surface of the aponeurotic origin of the sacrospinalis ; 



(2) from the posterior surface of the sacrum, as low as the fourth aperture ; 



(3) from the posterior sacro-iliac ligament ; (4) from the posterior superior 

 spine of the ilium ; and (5) from the mamillary processes of the lumbar 

 vertebrae. In the thoracic region it takes origin from the transverse processes 

 of the vertebrae, and in the cervical region from the articular processes of at 

 least four of the lower cervical vertebrae. Each of the bundles of which the 

 multifidus is composed passes upwards and is inserted into the whole length 

 of the lower border of the spine of the second, third, or fourth vertebra 

 above. The insertions extend from the fifth lumbar vertebra to the second 

 cervical vertebra. 



Musculi Rotatores. The rotator muscles are a series of small muscles 

 which are exposed when the multifidus is pulled aside. In the thoracic 

 region each muscle springs from the root of a transverse process, and is 

 inserted into the lamina of the vertebra immediately above, close to the 

 root of the spinous process. Somewhat similar muscles have been 

 described in the cervical and lumbar regions, and also a series of longer 

 and more superficial slips which connect alternate vertebrae with each 

 other. The multifidus and the rotatores are supplied by the posterior rami 

 of the spinal nerves. They turn the trunk and neck towards the opposite 

 side. 



Musculi Interspinales et Intertransversarii. The inter spinous muscles 

 can hardly be said to exist in the thoracic region, except in its upper 

 and lower parts, where they are present in a rudimentary condition. In 

 the neck they are arranged in pairs, occupying each interspinous interval, 

 with the exception of that between the first and second cervical vertebrae. 

 In the lumbar region also they are well marked and in pairs*: there, they are 

 attached to the whole length of the spinous processes. The intertransverse 

 muscles are strongly developed in the lumbar region, and occupy the entire 



