Overview
The mandible (mandibula) is the only movable bone of the skull. It is formed by two halves joined rostrally at the mandibular symphysis (symphysis mandibulae), which in cattle does not ossify: it stays fibrocartilaginous throughout life and allows slight movement between the two halves. Each half has a horizontal body, which carries the teeth, and a vertical ramus, which articulates with the temporal bone.
Body
- Incisive part (pars incisiva): carries three incisors and the canine on each side; in cattle the canine is incisiform. The eight teeth form a fan-shaped arcade that works against the dental pad of the upper jaw. In practice they are called centrals, first intermediates, second intermediates and corners.
- Interalveolar margin (margo interalveolaris): long toothless gap (diastema) between the canine and the first premolar.
- Molar part (pars molaris): three premolars (P2–P4) and three molars on each side, selenodont. The lower arcades are set closer together than the upper ones, so the teeth grind against each other with a side-to-side movement of the mandible.
- Mental foramen (foramen mentale): on the lateral surface of the body, in the region of the diastema; exit of the mental nerves and vessels.
Ramus
- Condylar process (processus condylaris): carries the head of the mandible, which articulates with the temporal bone at the temporomandibular joint.
- Coronoid process (processus coronoideus): tall; insertion of the temporalis muscle.
- Angle of the mandible: broad; insertion of the masseter on its lateral surface and of the medial pterygoid on its medial surface.
- Mandibular foramen (foramen mandibulae): on the medial surface of the ramus; entrance to the mandibular canal, which carries the inferior alveolar nerve and the vessels of the lower teeth.
Clinical relevance
- Actinomycosis (lumpy jaw): pyogranulomatous osteomyelitis caused by Actinomyces bovis, which enters through wounds of the oral mucosa caused by coarse forage or erupting teeth. It produces a hard, immovable bony swelling with draining tracts that discharge pus with yellowish granules; affected teeth loosen and chewing becomes difficult.
- Age estimation: the order of eruption of the permanent incisors, from centrals to corners, and their wear allow the age of the animal to be estimated.
- Dental wear and loss: in old cows, wear of the incisors and cheek teeth, and irregular or missing molars, impair prehension and chewing and lead to loss of body condition.