r 
ligament, from the mammillary processes of the lumbar vertebre, from the trans- 
verse processes of the thoracic vertebrae, and from the articular processes of the 
lower four cervical vertebrae. It is inserted into the spines of the vertebree up to 
and including the axis. Lying in contact with the vertebral laminz, the muscle 
is covered by the semispinalis. 
THE MUSCLES OF THE BACK. 371 
FourTH GROUP. 
The muscles bounding the suboccipital triangle are four in number—obliquus 
inferior, obliquus superior, rectus capitis*posticus major, and rectus capitis posticus 
minor. 
The obliquus inferior arises from the spine of the axis, and is inserted into the 
transverse process of the atlas. 
The obliquus superior arises from the transverse process of the atlas, and is 
inserted into the occipital bone external to the complexus and above the inferior 
curved line. 
The rectus capitis posticus major arises from the spine of the axis, and is 
inserted into the occipital bone beneath the obliquus superior and complexus, and 
below the inferior curved line. 
The rectus capitis posticus minor arises beneath the previous muscle from the 
spine of the atlas, and is inserted into the occipital bone below the inferior curved 
line and beneath the rectus capitis posticus major. 
These muscles are concealed by the complexus and splenius capitis; they enclose 
a triangular space (the suboccipital triangle) in which the vertebral artery, 
suboccipital nerve, and the posterior arch of the atlas are contained. The obliquus 
inferior is separated from the semispinalis muscle by the great occipital (second 
cervical) nerve. 
The rotatores dorsi are eleven pairs of small muscles occupying the vertebral 
eroove in the thoracic region, beneath the transverso-spinales, 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. 
The inter-spinales are bands of muscular fibres connecting together the spinous 
processes of the vertebree. 
The inter-transversales are slender slips extending between the transverse 
processes. They are double in the neck, the anterior divisions of the spinal nerves 
passing between them. 
The rectus capitis lateralis, extending from the transverse process of the atlas 
to the jugular process of the occipital bone, is homologous with the posterior of the 
two inter-transverse muscles. In the loin the inter-transversales muscles are usually 
double, but they are often absent, or are replaced by membrane. 
NERVE SUPPLY. 
With the exception of the vertebro-scapular and vertebro-humeral muscles (trapezius, 
latissimus dorsi, levator anguli scapule, rhomboidei), the muscles of the back are all supplied by 
the posterior primary divisions of the spinal nerves. In the upper part of the trunk the muscles 
are supplied mainly by the external branches ; in the lower part chiefly by the internal branches 
of the nerves. In the cervical and sacral regions a limited plexiform arrangement of the nerves 
occurs (posterior cervical and posterior sacral plexuses). 
ACTIONS. 
The action of these muscles is extremely complex. Not only do they act on the spinal 
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 spinal 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 pre- 
serving the erect position, and in the movements of the trunk they are assisted in large measure 
by muscles whose chief movements are referred to elsewhere (p. 350). 
1. Movements of the Spinal Column.—The movements of the vertebral column are flexion, 
extension, and lateral movement or rotation. 
