![]() In some cases, the mental spines are fused to form a single eminence, in others they are absent and their position is indicated merely by an irregularity of the surface. Immediately below these is a second pair of spines, or more frequently a median ridge or impression, for the origin of the geniohyoid. Near the lower part of the symphysis is a pair of laterally placed spines, termed the mental spines, which give origin to the genioglossus. įrom the inside, the mandible appears concave. Attached to this is the masseter muscle, the depressor labii inferioris and depressor anguli oris, and the platysma (from below). Running backward and upward from each mental tubercle is a faint ridge, the oblique line, which is continuous with the anterior border of the ramus. Below the second premolar tooth, on both sides, midway between the upper and lower borders of the body, are the mental foramen, for the passage of the mental vessels and nerve. ![]() ![]() Just above this, on both sides, the mentalis muscles attach to a depression called the incisive fossa. This ridge divides below and encloses a triangular eminence, the mental protuberance (the chin), the base of which is depressed in the center but raised on both sides to form the mental tubercle. From the outside, the mandible is marked in the midline by a faint ridge, indicating the mandibular symphysis, the line of junction of the two halves of the mandible, which fuse at about one year of age. The body of the mandible is curved, and the front part gives structure to the chin. The lingula is just above the mandibular foramen. The mandibular foramen is labeled on the right.
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