This group comprises only the buccinator muscle.

Buccinator muscle

The buccinator - named from its action, as it is the muscle used by the trumpeter (buccinator) - is a somewhat oval sheet of muscular fibre, distinct in its origin, but blending in front with the orbicularis oris. It forms a part of the third stratum of the facial muscles.

Origin

1. The outer surface of the alveolar process of the maxilla, above the last two molars;
2. the anterior border of the pterygo-maxillary ligament, a fibrous band or raphe extending from the hamular process of the internal pterygoid plate of the sphenoid bone to the back of the mylo-hyoid ridge of the mandible;
3. the outer surface of the alveolar process of the mandible below the last two molars.

Insertion

The outer part of the orbicularis oris.

Structure

It rises by fleshy fibres which run forwards in four sets. The upper set pass directly into the facial portion of the orbicularis oris which belongs to the upper lip; the next pass downwards and forwards to that which belongs to the lower lip; the third upwards and forwards, decussating with the second set to join he lower part of the orbicularis in the upper lip. Finally, a fourth set which pass from the mandible to the lower part of the facial portion of the orbicularis oris belonging to the lower lip.

The Deeper Layer of the Muscles of the Face and Neck.

Nerve-supply

The buccal branch of the lower division of the facial, which sends filaments into the back part of its outer surface; it is also pierced by the buccal branch of the inferior maxillary division of the fifth nerve on its way to supply the mucous membrane lining the cheek.

Action

1. To draw outwards the corner of the mouth, widening it and pressing the lips against the teeth;
2. to diminish the concavity of the cheek, compressing the air contained in it, as in using the blowpipe or playing the cornet; or forcing inwards the food when, in mastication, any portion of it has escaped into that part of the mouth which is external to the bicuspids and molar teeth.

Relations

Superficially, the skin, subcutaneous fat, Steno's duct, the zygo- maticus major, risorius, a large mass of fat (the buccal fat-pad) which separates the buccinator from the masseter, and a layer of deep fascia continuous with that which covers the upper part of the pharynx; deeply, the mucous membrane of the mouth. The upper part of the muscle is perforated by Steno's duct. The buccinator is almost continuous behind with the superior constrictor, from which it is only separated by the tendinous intersection of the pterygo-maxillary ligament.