Musculus scalenus
A deep lateral neck muscle that connects the cervical vertebrae to the first rib. Important for respiration (elevates the first rib during inspiration) and lateral neck flexion.
Origin: Transverse processes of cervical vertebrae C4-C7
Insertion: Cranial surface of the first rib
Action: Elevates the first rib during inspiration; lateral flexion of the neck
Innervation: Ventral branches of cervical spinal nerves (C5-C7)
In horses with respiratory difficulty (heaves/RAO), the scalenus works harder to expand the rib cage, contributing to accessory muscle fatigue.
In horses with respiratory difficulty (heaves/RAO), the scalenus works harder to expand the rib cage, contributing to accessory muscle fatigue. Signs include: Visible effort during breathing; flared nostrils; increased respiratory rate; abdominal push during expiration (heave line); fatigue during exercise.
See the Scalenus on our interactive 3D horse model. Open 3D Model