Musculus genioglossus
The genioglossus is the largest and most important extrinsic muscle of the tongue. It originates from the medial surface of the mandibular symphysis (genial tubercle) and inserts along the entire length of the tongue from base to tip, with some fibers also attaching to the basihyoid bone. It is a fan-shaped muscle whose primary actions are to protrude the tongue and depress it. It is critical for food gathering, manipulation, and the initial stages of swallowing. Innervation is via the hypoglossal nerve (CN XII). Damage to the hypoglossal nerve or the muscle itself can impair the horse’s ability to move food in the mouth and may contribute to difficulty eating or, in some cases, upper-airway instability at exercise.
Origin: Medial surface of the mandibular symphysis (genial tubercle)
Insertion: Entire length of the tongue from base to tip; also attaches to the basihyoid bone
Action: Protrudes the tongue; depresses the tongue; essential for food gathering and manipulation during eating
Innervation: Hypoglossal nerve (CN XII)
Hypoglossal-nerve lesions produce tongue weakness or deviation. The genioglossus is the main protruder of the tongue; unilateral paralysis causes the tongue to deviate toward the affected side when protruded. Severe tongue weakness can be seen in equine motor neuron disease or other neurologic conditions.
Bilateral hypoglossal nerve damage causes complete tongue paralysis. The tongue hangs from the mouth and the horse cannot eat or drink. Often from guttural pouch pathology affecting CN XII bilaterally
A horse that drops feed, has difficulty manipulating hay or grain, or shows tongue deviation needs dental and neurologic evaluation. Sudden tongue weakness after trauma to the head or neck should be checked promptly.
Bilateral hypoglossal nerve damage causes complete tongue paralysis. The tongue hangs from the mouth and the horse cannot eat or drink. Often from guttural pouch pathology affecting CN XII bilaterally. Signs include: Tongue protruding from the mouth; inability to retract the tongue; cannot eat or drink; drooling; rapid weight loss; often accompanied by other cranial nerve deficits.
Hypoglossal-nerve lesions produce tongue weakness or deviation. The genioglossus is the main protruder of the tongue; unilateral paralysis causes the tongue to deviate toward the affected side when protruded. Severe tongue weakness can be seen in equine motor neuron disease or other neurologic conditions.
A horse that drops feed, has difficulty manipulating hay or grain, or shows tongue deviation needs dental and neurologic evaluation. Sudden tongue weakness after trauma to the head or neck should be checked promptly.
See the Genioglossus on our interactive 3D horse model. Open 3D Model