Yousun Koh
Muscles of thoracic wall (Anterior view) (English)
Muscles of thoracic wall (Anterior view) (English)
The extrinsic muscles of the thoracic wall include the subclavius, pectoralis maj…or and minor and serratus anterior muscles. The short, triangular subclavius muscle is located beneath the clavicle and mainly functions in anchoring and depressing the bone. The large pectoralis major muscle arises from three heads (clavicular, sternocostal and abdominal) which unite before inserting into the intertubercular sulcus of the humerus. Deep to the pectoralis major muscle, is the smaller pectoralis minor muscle. The pectoralis major primarily flexes, adducts and internally rotates the arm at the shoulder joint on contraction, while the pectoralis minor muscle stabilizes and draws the scapula anteroinferiorly. Located along the anterolateral aspect of the thoracic wall is the large fan shaped serratus anterior muscle. This muscle primarily functions to rotate and draw the scapula anterolaterally. All of the extrinsic muscles of the thoracic wall participate in elevation of the rib cage during forced inspiration as a secondary function.Intrinsic muscles evident from this anterior view include the intercostal, subcostal and transversus thoracis muscles. Lying beneath the large extrinsic muscles of the thoracic wall are the intercostal muscles (external, internal and innermost intercostal muscles). These muscles are located within the intercostal spaces and function to elevate, stabilize or depress the thoracic cage and therefore facilitate breathing movements. The subcostal muscles are bands of muscle located on the internal surface of the lower ribs, sharing a plane with the innermost intercostals. They support the intercostal spaces and thoracic cage, and depress the ribs during forced expiration. Also located along the internal aspect of the thoracic cage is the transversus thoracis muscle. This is a weak muscle of the rib cage which assists in expiration.
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