Musculi intercostales interni
Deep to external intercostals with fibers running craniodorsally. Assist active expiration by drawing ribs caudally and inward. Important during exercise and in respiratory disease.
Origin: Cranial border of each rib (internal surface)
Insertion: Caudal border of the adjacent cranial rib
Action: Depress the ribs during active expiration
Innervation: Intercostal nerves
In heaves, internal intercostals work overtime for forced expiration, contributing to the heave line and rib cage reshaping.
In heaves, internal intercostals work overtime for forced expiration, contributing to the heave line and rib cage reshaping. Signs include: Visible effort during expiration; intercostal spaces sucked in during labored breathing; chronic cough; exercise intolerance; weight loss.
See the Internal Intercostals on our interactive 3D horse model. Open 3D Model