Internal intercostal muscles
Musculi intercostales interni
Definition
The internal intercostal muscles (Musculi intercostales interni) are fibers that run from the cranial aspect of one rib to the caudal aspect of the preceding rib in a cranioventral direction (perpendicular to the fibers of the external intercostal muscles). These muscles lie lateral to the intercostal nerve and assist expiration.
In dogs:
These muscle fibers cover the inter-costal space from the vertebral column, where they leave free a small trangular space adjacent to the vertebrae, to the distal end of the ribs, including the cartilaginous portion.
Origin: cranial border of ribs
Insertion: caudal border and inner face of preceding rib
Action: expiration, to draw the ribs together so as to narrow the thoracic cavity
Nerve: Muscular branches of intercostal nerves one to twelve.
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