THE masseter muscle originates on the zygomatic arch and the zygomatic process of the maxilla and is inserted into the lateral aspect of the angle and ramus of the mandible. When the muscle is activated by a clenching of the teeth, its belly can be seen bulging under the skin, and the anterior edge may easily be palpated in the substance of the buccal wall. In a gaunt subject or in one whose mandibular angles flare outward the masseter muscles may be prominent.
At times the prominences may be such that the subject will seem to have bilateral swellings of the jaw, and epidemic parotitis will be suspected. This has occurred several times during routine examinations of troops for communicable diseases and has resulted in unwarranted hospitalizations and isolations. In each instance in which this occurred, a story of habitual clenching of the jaws repeatedly when emotionally disturbed or under