THE MUSCLES OF THE BACK. 445 



inserted into the occipital bone below the inferior nuchal line medial to and beneath 

 the rectus capitis posterior major (Fig. 396, p. 444). 



Nerve-Supply. Posterior ramus of the first cervical (suboccipital) nerve. 

 Actions. Elevation, lateral movement and rotation of the head. 



Mm. Rotatores. The rotatores are eleven pairs of small muscles occupying 

 the vertebral groove in the thoracic region, deep to the semispinalis dorsi, of which 

 they form the deepest fibres. Each consists of a small slip arising from the 

 transverse process and inserted into the lamina of the vertebra directly above. 



Nerve -Supply. Posterior rami of the thoracic nerves. 

 Actions. Extension and rotation of the vertebral column. 



Mm. Interspinales. The interspinales are bands of muscular fibres connect- 

 ing together the spinous processes of the vertebrae. 



Nerve-Supply. Posterior rami of the spinal nerves. 

 Action. Extension of the vertebral column. 



Mm. Intertransversarii. The intertransversarii are slender slips extending 

 between the transverse processes. They are double in the neck, the anterior 

 branches of the spinal nerves passing between them. In the loin the inter- transverse 

 muscles are usually double, but they are often absent, or are replaced by membrane. 



Nerve-Supply. Anterior rami of the spinal nerves. 



Actions. Lateral movement and rotation of the vertebral column. 



Mm. Rectus Capitis Lateralis. The rectus capitis lateralis, extending from 

 the transverse process of the atlas to the jugular process of the occipital bone (Fig. 

 396, p. 444), is homologous with the posterior of the two inter- transverse muscles. 



Nerve-Supply. Anterior ramus of the first cervical (suboccipital) nerve. 



Action. Lateral movement and rotation of the head. The action of these muscles is 

 extremely complex. Not only do they act on the vertebral column, ribs, head, and pelvis, 

 in conjunction with other muscles, but some of them act also in relation to the movements of 

 the limbs as well. In this section will be given an analysis of their movements in relation to 

 the vertebral column, head, and pelvis. The movements of the limbs and of the ribs (respiration) 

 are dealt with in other sections. The chief muscles are engaged in preserving the erect position, 

 and in the movements of the trunk they are assisted in large measure by muscles whose chief 

 actions are referred to elsewhere. 



1. Movements of the Vertebral Column. The movements of the vertebral column are 

 flexion, extension, and lateral movement or rotation. These movements occur in all regions 

 neck, thorax, and loin ; flexion and extension and lateral movement are most limited in the 

 region of the thorax ; while rotation is most limited in the region of the loin. 



b. Lateral Movement (Rotation). 



Levator scapulae 



Serrati posteriores 



Splenius cervicis 



Sacrospinalis 



Semispinalis capitis 



Semispinalis (dorsi and cervicis) 



Multifidus 



Rotatores 



Intertransversarii 



Longus colli 



Longus capitis 



Scaleni, anterior, inedius, posterior 



Psoas (major and minor) 



Quadratus lumborum 



Obliquus abdominis externus 



Obliquus internus 



Transversus 



Rectus 



Pyramidalis ,, 



