Buccinator muscle

The buccinator muscle is flat, located in the cheek, and extends parallel to the main axis of the mouth, laterally closing the oral cavity. The region between the masseter and the orbicularis oris muscles forms the anatomical base of the buccal region.

Conformation: This muscle consists of two parts. The molar part, which is constant, is made up of longitudinal fibers and extends from the maxillary tuberosity and the mandibular branch to the commissural region of the orbicularis muscle of the mouth. This part is the only one present in humans. In most mammals, it is covered on its surface, rostrally to the masseter, by a buccal part whose fibers extend from one jaw to the other. This buccal part has a more or less pronounced longitudinal raphe depending on the species, giving it a typically penniform appearance. It is more developed in ungulates than in carnivores. In carnivores, the buccal part occupies little space behind the angle of the mouth but extends into the thickness of both lips. The buccinator is thinner and weaker in carnivores compared to its configuration in herbivores.

Insertions: The molar part originates from the maxillary tuberosity and the alveolar margin of the maxilla in the region of the molar teeth; from a fibrous lamina extending from the pterygoid hook to the rostral margin of the mandibular branch; from the buccopharyngeal fascia; from the lateral underside of the mandibular alveolar margin, opposite the last molar teeth, and from the adjacent part of the rostral margin of this bone's ramus. The molar part ends in multiple small tendinous bundles, which blend with the orbicularis of the mouthmuscle or attach to the deep surface of the skin in the commissural region.

Relations: The caudal part is covered by the masseter muscle. In front of this, the buccinator is crossed superficially by the facial artery and vein, and then it passes transversely, at a point that varies slightly between species. For the rest of its length, it is separated from the skin by the zygomatic, caninus, nasolabial levator muscles, and, in ruminants, the malar muscle. Finally, it is covered by the terminal expansion of the facial part of the platysma. The dorsal edge is partially covered by the upper molar glands; the buccal nerve and its satellite vessels follow it in depth. The ventral edge is bordered in ungulates by the depressor labii inferioris muscle; it is also in relation to the lower molar glands or buccal glands, varying by species. The deep surface is lined by the buccal mucosa, which adheres intimately to it.

Functions: This muscle pulls the angle of the mouth backward and laterally. Its most important function is to empty the buccal vestibule of any substances that may be lodged there. It pushes food particles that escape during chewing back under the molar arches.

Vessels and nerves: This muscle is supplied by the buccal, facial, and labial arteries. Motor innervation is provided by the two buccal branches of the facial nerve, primarily the dorsal buccal branch. Sensory fibers are supplied by the buccal nerve.

Variations:

• In equines, the buccinator muscle is equipped with a well-developed and distinctly penniform buccal part. The parotid duct passes through it at the level of the third upper premolar. Its dorsal edge is long and covered by the upper buccal glands, while its ventral edge covers the lower buccal glands.

• In cattle, the buccinator muscle is thick and very wide, covering a large portion of the cheek. Its buccal part is extremely extended and rises under the masseter, although its raphe is not very pronounced and is limited to its rostral half, near the dorsal edge. The muscle is crossed by the termination of the parotid duct at the level of the root of the first upper molar. The dorsal edge is bordered by the depressor labii superioris muscle, and the ventral edge is intimately joined to the depressor labii inferioris muscle. Its surface is bordered by particularly developed upper buccal glands and a group of medium-sized buccal glands.

• In pigs, the buccinator muscle is relatively short, and its buccal part is poorly distinct but extends to the deep surface of the orbicularis of the mouth, especially in the upper lip.

• In dogs, the buccinator muscle is wide and thin. Its buccal part extends under the masseter; a poorly defined raphe divides it into a larger dorsal part and a weaker ventral part. The first attaches above the first three premolars and continues into the upper lip to the deep surface of the orbicularis oris muscle. The second starts below the first two premolars and the lower canine and extends less far into the lower lip; it compensates for the absence of the depressor labii inferioris muscle.

• In cats, the buccinator muscle is wide, short, thin, and very weak. Its molar part comes from the buccopharyngeal fascia but has nearly lost its insertions on the jaws. The parotid duct passes through it at the level of the upper carnassial tooth.

• In rabbits, the buccinator muscle is very extended, wide, and thick. Its buccal part is long, and its raphe divides it into two equal parts.