Musculus orbicularis oris
The orbicularis oris is a circular sphincter muscle surrounding the mouth. Its fibers are intrinsic to the lips and blend with surrounding facial muscles; it has no bony insertion. Its actions are to close and purse the lips and aid in food prehension. It is innervated by the buccal branches of the facial nerve (CN VII). It is important for grasping food and for lip seal during swallowing. In foals it is essential for suckling.
Origin: Muscle fibers intrinsic to the lips, blending with surrounding facial muscles
Insertion: Skin and mucosa of the lips (circular, no bony insertion)
Action: Closes and purses the lips; aids in food prehension
Innervation: Buccal branches of facial nerve (CN VII)
Dysfunction can occur with facial nerve injury, leading to lip droop or difficulty grasping feed. Relevant in evaluations of facial nerve function and oral prehension.
## Overview Bit-related lip injuries are traumatic lesions of the commissures (corners) of the mouth, the bars, or adjacent buccal mucosa caused by pressure or movement of the bit. They range from mi
## Overview Facial nerve paralysis is loss of function of the facial nerve (cranial nerve VII), which controls the muscles of facial expression. It produces lip droop, ear droop, inability to blink,
Difficulty grasping feed, lip droop, or asymmetry of the muzzle after trauma should be evaluated. Foals that cannot suckle need prompt attention.
## Overview Bit-related lip injuries are traumatic lesions of the commissures (corners) of the mouth, the bars, or adjacent buccal mucosa caused by pressure or movement of the bit. They range from mild bruising to open ulcers and are common in competition horses. Chronic lesions can lead to depigmentation or scarring at the lip corners. ## Causes Bit design, size, and rider hand pressure are the main factors. Studies show higher lesion rates with very thin or very thick bits, certain curb bits, and in some disciplines or breeds. Poor dental care or sharp enamel points can worsen soft-tissue trauma. ## Diagnosis Visual inspection of the mouth after removing the bit reveals bruising, erosions, or ulcers, most often at the inner lip commissures. Grading systems used in research classify lesions as mild, moderate, or severe. ## Treatment Remove the offending bit, allow rest from bitting, and keep the area clean. Most lesions heal within days to a couple of weeks once pressure is eliminated. Severe or infected wounds may need veterinary attention. Address dental overgrowths and reassess bit fit and rider technique. ## Recovery and Prognosis Prognosis is excellent for soft-tissue healing. Recurrent injury is likely if the same bit and handling continue. Chronic depigmentation may remain as a cosmetic change. ## Prevention Choose an appropriately sized and designed bit, maintain regular dental care, and use light, consistent rein contact. Routine mouth checks after work help detect problems early. Signs include: bruising or ulcers at the corners of the mouth; blood on the bit; reluctance to accept the bit; depigmentation of the lip commissures in chronic cases
## Overview Facial nerve paralysis is loss of function of the facial nerve (cranial nerve VII), which controls the muscles of facial expression. It produces lip droop, ear droop, inability to blink, and muzzle deviation toward the normal side. Trauma and post-anesthetic neuropathy are common causes. ## Causes Trauma to the nerve as it crosses the face, prolonged halter pressure, or central lesions. Inflammation or infection can also be involved. ## Diagnosis Clinical observation of asymmetric facial movement. Neurologic examination localizes the lesion. Further diagnostics if a central cause is suspected. ## Treatment Anti-inflammatories if acute, eye protection to prevent corneal ulcers, and time for nerve recovery. Physical therapy or acupuncture is sometimes used. ## Recovery and Prognosis Variable. Many traumatic cases improve over weeks to months. Complete recovery is not guaranteed. ## Prevention Careful halter fit and avoidance of facial trauma. Signs include: lip droop; ear droop; inability to blink; muzzle pulled to the normal side; food falling from the mouth; drooling
Dysfunction can occur with facial nerve injury, leading to lip droop or difficulty grasping feed. Relevant in evaluations of facial nerve function and oral prehension.
Difficulty grasping feed, lip droop, or asymmetry of the muzzle after trauma should be evaluated. Foals that cannot suckle need prompt attention.
See the Orbicularis Oris on our interactive 3D horse model. Open 3D Model