Human Anatomy, Part 1 - K. A. Dyubenko, A. K. Kolomiytsev, Yu. B. Chaykovsky 2002

Special Part
Myology, myologia [the study of muscles] — Muscles and Fasciae of the Trunk
Muscles and Fasciae of the Thorax — Intrinsic Muscles of the Chest

1. External intercostal Muscles, mm. intercostales externi.

2. Internal intercostal muscles, mm. intercostales interni.

3. Subcostal muscles, mm. subcostales.

4. Transverse thoracic Muscle, m. transversus thoracis.

1. External intercostal muscles, mm. intercostales externi (see Fig. 128) originate from the lower margins of the Ribs, run obliquely downward and forward, and attach to the upper margins of the underlying ribs. They are absent in the region of the costal cartilages, where their place is taken by the external intercostal membrane, membrana intercostalis externa.

Function: they participate in the act of breathing.

Blood supply: aa. intercostales posteriores, thoracica interna, musculophrenica.

Innervation: nn. intercostales (Th I–Th XI).

2. Internal intercostal muscles, mm. intercostales interni — posteriorly they reach only the angles of the ribs, and anteriorly they extend to the ends of the intercostal spaces (see Fig. 130). They originate from the upper margins of the ribs, run obliquely upward and forward, and attach to the lower margins of the overlying ribs. They are absent in the posterior part of the intercostal space, behind the angles of the ribs, where the internal intercostal membrane, membrana intercostalis interna, is located.

Function: they participate in the act of breathing.

Blood supply: aa. intercostales posteriores, thoracica interna, musculophrenica.

Innervation: nn. intercostales (Th I–Th XII).

3. Subcostal muscles, mm. subcostales — located on the inner surface of the thoracic wall in its posterior region. They have the same origin and direction as the internal intercostal muscles, but differ in that their fibers span across one rib. They are best developed in the lower half of the Thorax.

Function: they participate in the act of breathing.

Blood supply: aa. intercostales posteriores.

Innervation: nn. intercostales (Th I–Th XII).

4. Transverse thoracic muscle, m. transversus thoracis — lies on the posterior surface of the cartilages of the III–VI ribs. It originates from the processus xiphoideus and the lower half of the corpus sterni, runs laterally and upward, and attaches by digitations to the II–VI ribs at the transition of the bony part of the ribs into the cartilaginous part.

Function: it participates in the act of breathing.

Blood supply: a. thoracica interna.

Innervation: nn. intercostales (Th I–Th VI).