Overview
The mandible (mandibula) is the only movable bone of the skull. It is made of two halves that fuse at the mandibular symphysis during the first months of life, so in the adult it is a single bone. Each half has an incisive part, which holds the incisors and the canine, a body carrying the cheek teeth and a vertical ramus that articulates with the skull. In the horse the ramus is tall and the mandibular angle very wide, for the attachment of the powerful masseter.
Key features
- Interalveolar margin (margo interalveolaris): the interdental space (the "bars") between the canine or incisors and the first cheek tooth. It is covered only by gum and is where the bit rests.
- Notch for the facial vessels (incisura vasorum facialium): on the ventral border, rostral to the angle; the facial artery and vein and the parotid duct cross it onto the face. The horse's pulse is taken here.
- Mental foramen (foramen mentale): on the lateral surface of the incisive part; exit of the mental nerve.
- Mandibular foramen (foramen mandibulae): on the medial surface of the ramus; entry of the inferior alveolar nerve into the mandibular canal.
- Coronoid process: tall and narrow; it rises into the temporal fossa and receives the temporalis.
- Condylar process: articulates with the temporal bone at the temporomandibular joint, which has an articular disc and allows the wide side-to-side movements of chewing.
Clinical relevance
- Injuries to the bars: a poorly fitted bit or rough use of the reins can injure the gum and the bone of the interdental space.
- Fractures of the incisive part: common when the horse bites a fixed object and pulls back; they usually have a good prognosis with wire fixation.
- Eruption bumps: in young horses, firm swellings on the ventral border below the erupting premolars; they normally resolve on their own.
- Nerve blocks: the mental and inferior alveolar nerves are anaesthetised for dental procedures.