internal intercostal (muscle)
in·ter·nal in·ter·cos·tal (mus·cle)[TA]
flat muscle of thorax arising from lower border of rib and passes obliquely downward and backward to be inserted into upper border of rib below; action, contract during expiration, also maintain tension in the intercostal spaces to resist mediolateral movement; nerve supply, intercostal.
Synonym(s): musculus intercostalis internus [TA]
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