In human anatomy, the thoracic diaphragm
, or simply the diaphragm
(Ancient Greek: diáphragma
"partition"), is a sheet of internal skeletal muscle
that extends across the bottom of the thoracic cavity. The diaphragm separates the thoracic cavity containing the heart and lungs, from the abdominal cavity and performs an important function in respiration: as the diaphragm contracts, the volume of the thoracic cavity increases and air is drawn into the lungs.
External intercostal muscles
The external intercostal muscles, or external intercostals (Intercostales externi) are eleven in number on either side.
Intercostal muscles are several groups of muscles that run between the ribs, and help form and move the chest wall. The intercostal muscles are mainly involved in the mechanical aspect of breathing. These muscles help expand and shrink the size of the chest cavity to facilitate breathing.
The scalene muscles (from Greek σκαληνός, or skalenos, meaning uneven as the pairs are all of differing length) are a group of three pairs of muscles in the lateral neck, namely the anterior scalene, middle scalene, and posterior scalene. They are innervated by the fourth, fifth, and sixth cervical spinal nerves (C4-C6).
Transversus thoracis muscle
The transversus thoracis muscle lies internal to the thoracic cage, anteriorly. It is a thin plane of muscular and tendinous fibers, situated upon the inner surface of the front wall of the chest. It is in the same layer as the subcostal muscles and the innermost intercostal muscles.