human_reference_atlas Homo sapiens intercostal muscle external intercostal muscle http://upload.wikimedia.org/wikipedia/commons/f/f2/Gray411.png intercostals external muscle Wikipedia:External_intercostal_muscles EHDAA2:0000465 An intercostal muscle that aids in quiet and forced inhalation via elevation of the ribs, and expanding the transverse dimensions of the thoracic cavity. FMA:9756 UBERON:0005441 Behind the thorax, the lateral group (of muscles in reptiles and mammals) remains essentially as for amphibians. (It breaks into three sheet-like layers: external oblique muscle, the internal oblique, and the transversus). More anteriorly, however, the ribs, now enlarged, penetrate and alter this group of muscles. The transversus is excluded from the thorax and the external and internal obliques become, respectively, the external and internal intercostal muscles, which contribute to the new function of ventilation of the lungs.[well established][VHOG] intercostals external NCIT:C32561 intercostales externi EHDAA:8260 intercostalis externus musculi intercostales externi intercostales externi muscle external intercostal muscle AS VHOG:0000904 intercostales externus uberon external intercostal muscle EMAPA:18522 SCTID:244878003 MA:0002325 external intercostal muscle UMLS:C1744535 intercostal muscle external layer external intercostals intercostales externi muscles They extend from the tubercles of the ribs behind, to the cartilages of the ribs in front, where they end in thin membranes, the anterior intercostal membranes, which are continued forward to the sternum. Each arises from the lower border of a rib, and is inserted into the upper border of the rib below. In the two lower spaces they extend to the ends of the cartilages, and in the upper two or three spaces they do not quite reach the ends of the ribs. They are thicker than the Intercostales interni, and their fibers are directed obliquely downward and laterally on the back of the thorax, and downward, forward, and medially on the front (the example is often used of sticking one's hands in their pocket and noting the direction of the fingers pointing downward and medially) thoracic wall muscle