Mentalis muscle

The mentalis muscle in humans consists of the mentalis muscle and the transverse muscle of the chin. The human chin is more developed than that of other domestic mammals, which lack a chin. However, equids and ruminants have, behind the lower lip, under the incisive part of the mandible, a rounded protuberance called the "chin tuft."

Conformation: In humans, the transverse muscle of the chin forms, beneath the skin to which it adheres, the protuberance of the "chin tuft." It is unpaired and bilobed, with fibers spreading on either side of a small raphe attached to the mandibular symphysis. The mentalis muscle itself extends under the gum and attaches to the mandible, at the level of the alveoli of the incisor teeth.

In domestic mammals, a visible muscular nucleus is present, particularly in the chin tuft of ruminants and equines, mixed with connective and adipose tissues. This nucleus is attached to the mandible by two small mental muscles. In carnivores and rabbits, although there is no distinct chin protrusion, the mentalis muscle is developed. In pigs, it is broad and strong.

Insertions: The mental muscle originates in the incisor fossa of the mandible and inserts into the skin of the chin.

Functions: In humans, this muscle lifts the skin of the chin and elevates the lower lip. In horses, ruminants, and pigs, it serves to raise the lower lip in synergy with the orbicularis muscle. Additionally, in horses, it contributes to the erection of tactile hairs.

Variations:

• In horses, the mentalis muscle is weak and narrow, but the transverse part forms a relatively important muscular-adipose core, that creates the protuberance of the chin tuft.

• In cattle, the mentalis muscle is weak; it takes the form of a bundle attaching to the mandible between the mental foramen and the alveolus of the lateral incisor. Its fibers fade into a poorly defined chin tuft, nearly independent of the one on the opposite side.

• In pigs, the mentalis muscle is large and strong.

• In dogs, the mentalis muscle is arranged similarly to that of pigs. However, the chin tuft is somewhat better developed, and the chin is smaller.

• In cats, the mentalis muscle does not present any particular characteristic.

• In rabbits, the mentalis muscle is well developed, although the chin tuft is not very distinct.