The muscles of the chest wall

The muscles of the chest wall can be divided into a surface and a lower layer. The surface layer serves the upper limbs, whereas the lower layer between the ribs (costae) serves above all to seal the chest (thorax) and to support respiration.

The large pectoral muscle (musculus pectoralis major) extends from the collarbone (clavicula), breastbone (sternum) and from the abdomen fasciae to the upper arm (upper arm). It pulls the upper arm in to the body and turns it inwards. When the arm is fixed, it supports it when breathing in.

The small pectoral muscle (musculus pectoralis minor) extends from the third and fourth rib to the coracoid process (processus coracoideus) of the shoulder blade (scapula). It pulls the pectoral girdle forwards and, together with the large pectoral muscle, lifts the ribs when breathing in.

The serratus anterior muscle (musculus serratus anterior) is a saw-tooth plumed muscle, which extends from the first to ninth rib to the inner edge of the shoulder blade (margo medialis scapulae). It lifts the ribs when breathing in. In addition, it pushes the shoulder blade forwards and, together with the trapezius muscle (musculus trapezius), lifts the arm above the horizontal plane.

The sternomastoid muscle (musculus sternocleidomastoideus) originates in the collarbone and breastbone, and extends to the occipital bone in the area of the mastoid process (processus mastoideus). It can raise the chest.

The intercostal muscles (intercostalmuskeln) consist of two layers, whose fibers cross each other almost at right angles. The intercostal muscles starting at the inner edge of the costal arches are referred to as inner muscles (musculi intercostales interni). They lower the ribs on breathing out. The outer intercostal muscles (musculi intercostales externi) lift the ribs on breathing in. Finally there is another group of intercostal muscles, the innermost (musculi intercostales intimi). They are separated from the inner muscles by the intercostals nerves and are also respiratory muscles.

The scalariform muscles (musculi scaleni) continue the intercostal muscles toward the head. They originate at the transverse processes at the cervical vertebrae and extend to the first and second rib. They play an important rule in calm breathing, but also bend the cervical vertebrae (vertebrae cervicales) to the side and to the front.