| I. | Internal intercostals | ||
| with the infracostals. | |||
| II. | Triangularis sterni. | ||
| { Transversalis. | |||
| III. | Abdominal muscles | { Rectus. | |
| { Internal oblique. | |||
| { External oblique. | |||
There are many accessory muscles which aid in violent respiratory movements, both inspiratory and expiratory. All the muscles which elevate the scapula may act through it upon the ribs; the three scalene muscles act directly upon the first rib.
The principal muscles of inspiration may be assisted by the
| I. | Serratus posticus superior. | |
| II. | Serratus magnus. | |
| III. | Pectoralis major. | |
| IV. | Pectoralis minor. | |
The principal muscles of expiration may be aided by the following muscles:—
| I. | Serratus posticus inferior, | |
| II. | Longissimus dorsi, | |
| III. | Sacro lumbalis, | |
and all the muscles which tend to depress the ribs.
