external intercostal muscle

ex·ter·nal in·ter·cos·tal mus·cle

(eks-tĕr'nal in'tĕr-kos'tăl mŭs'ĕl) Flat muscle of thorax arising from lower border of one rib and passing obliquely downward and forward to be inserted into upper border of rib below; action, contracts during inspiration to elevate ribs; also serves to maintain tension in intercostal spaces to resist inward movement during inspiration; nerve supply, intercostal.
Synonym(s): musculus intercostalis externus.