The Muscles of the Abdomen are arranged in three directions -longitudinal, transverse, and oblique. The longitudinal ones straight up the front, flex the trunk, helped by the oblique ones when both sides act together. When the oblique muscles act singly, rotation of the trunk takes place. The longitudinal muscles on the posterior wall of the abdomen extend the spine when both act together. Acting singly, they flex the spine laterally. The transverse muscles of the abdominal wall are mainly used to keep the contents of the abdomen in place and to add to the strength of the wall, but help in flexion with the others.

Fig. 36. Muscles of the Abdomen.

Fig. 36. - Muscles of the Abdomen.

Some of the muscles causing flexion and extension of the cervical part of the spine are situated in the neck and attached to the head; these must not be confused with the muscles that specially move the head on the spine.

(For Flexion and Extension of Spinal Column, see pp. 94 and 95.)

The movement of lateral flexion of the spinal column takes place by the muscles of flexion and extension acting together on one side. In the cervical region, however, there are a group of muscles which cause lateral flexion of that part.

Action .

Muscle.

Origin.

Insertion.

Nerve-supply.

Lateral flexion

Scalenus anticus

From the transverse processes of the third, fourth, fifth, and sixth cervical vertebrae

The scalene tubercle and ridge'on the first rib

Anterior primary divisions of lower four or five cervical nerves

Scalenus medius

From the transverse processes of the lower cervical vertebra (second to sixth inclusive)

On the first rib behind the groove for the subclavian artery

Same as above

Scalenus posticus

From the transverse processes of the fourth, fifth, and sixth cervical vertebrae

The outer surface of the second rib about the middle

Same above