Muscle Monday! 
Today’s feature is the Masseter
Origin and Insertion: Originating from the zygomatic ridge or facial crest of the maxilla (upper mandible) by strong broad tendon. The insertion is into the lateral external surface of the upper broad portion of the inferior maxilla or mandible (lower jaw).
Action: When engaged the masseter brings the teeth of the lower jaw to meet the upper, sometimes at force and is the single most powerful muscle that is engaged in mastication. It is the power behind the grinding action of the teeth for the cheek teeth, working unilaterally it can engage and achieve a sideways movement. Some regard this muscle to be one of the most powerful of the entire body, not just of the head and jaw.
Problems: Teeth concerns will effect this muscle and in many cases will be larger on one side of the horse due to the sideways action of chewing. Pull-backs with the halter may initiate trauma to the mandibular nerve that could potentially lead to head shaking, head shyness, facial paralysis and also muscular atrophy. If there is significant pain from the masseter the horse may loose weight due to inability or reluctance to chew.
Comments: This muscle can consist of 2 or more layers or compartments and have a strong aponeurosis in the caudal area, and may show layers of tendinous tissue permeating throughout. Beneficial to have teeth checked in the case of atrophy of the 
masseter.
Its interesting to note that our model is the gorgeous 27 year old arabian mare, Azaria, and if you look closely you can see that her masseter muscle is atrophied. This is due to a) her age and also b) that she only has 3 molar teeth remaining, meaning that mastication is at a minimal for her.
Melissa Longhurst is a certified Equine Body Worker (EEBW) and Equi-Tape Therapist working in the
Mackay & Whitsunday’s region of Queensland.
I welcome you to share the articles posted on this site but do request that original works are credited.
Equine Massage should not be used as a substitute for veterinary care. If in doubt of your horses’ health or well being, Melissa will refer you to your preferred veterinarian prior to commencing any bodywork. Horses under the care of a veterinarian should first be cleared by the attending veterinarian to ensure that massage is appropriate for the horse at this time