294 A MANUAL OF ANATOMY 



deep branch of the ramus cervicahs princeps of the occipital from 

 the external carotid. Above the level of the axis spine it covers 

 the recti capitis postici and obliqui capitis muscles, and forms the 

 roof of the suboccipital triangle. 



Semispinalis Dorsi — Origin. — ^The extremities of the transverse 

 processes of thoracic vertebrae from the sixth to the tenth inclusive. 



Insertion. — ^The spines of the last two cervical and upper four 

 thoracic vertebrae. 



Semispinalis Colli — Origin. — ^The extremities of the transverse 

 processes of the upper five thoracic vertebrae. 



Insertion. — The spines of cervical vertebrae from the second to 

 the fifth inclusive. 



The bundle of fibres inserted into the axis spine is the largest, 

 and the bundles overlap one another from above downwards. 



Nerve-supply of the Semispinales. — The posterior primary divisions 

 of the cervical and upper thoracic nerves. 



The fibres of the two muscles are directed upwards and inwards. 



Action. — ^The muscles are extensors and lateral flexors of the 

 vertebral column. The semispinalis colli and the cervical portion 

 of the semispinalis dorsi also rotate the cervical vertebrae towards 

 the opposite side. 



Multifidus Spinae. — This muscle lies deeply in the groove by the 

 sides of the spines of the vertebrae. 



Origin. — (i) The sacral groove, and the deep surface of the tendon 

 of the erector spinae ; (2) the posterior sacro-iliac ligament, and the 

 inner lip of the iliac crest at its back part ; (3) the mammillary 

 tubercles of the lumbar vertebrae ; (4) the transverse processes of 

 the thoracic vertebrae ; and (5) the articular processes of the lower 

 four cervical vertebrae. 



Insertion. — The spines of the vertebrae from root to tip. 



The superficial fibres from any given origin pass over three or four 

 vertebrae before taking insertion, the succeeding fibres pass over 

 two or three, and the deeper fibres pass over one. 



Nerve-supply. — ^The posterior primary divisions of the spinal nerves. 



Action. — ^The muscle is an extensor and lateral flexor of the spinal 

 column, producing at the same time rotation towards the opposite 

 side in the cervical and thoracic regions. 



Rotatores Spinae. — These muscles are really the deepest fibres of 

 the multifidus spinae in the thoracic region. They are eleven in 

 number. 



Origin. — The upper and back part of a transverse process. 



Insertion. — The lower border of the lamina of the vertebra imme- 

 diately above. 



Nerve-supply. — ^The posterior primary divisions of the spinal nerves. 



Action. — To rotate the vertebrae towards the opposite side. 



Interspinales. — These muscles are usually confined to the cervical 

 and lumbar regions, where they are arranged in pairs between the 

 spines, one on either side of the middle line. In the neck they 

 are limited to the region of the apices of the spines, but in the 



