Mastication Muscles

[Continued from above] . . . for speech) the province of four intrinsic tongue muscles.

The masseter muscle is a thick quadrilateral muscle located in the cheek. It is needed for mastication (chewing) and performs when it closes the jaws. It is made up of two parts: superficial and deep. The larger, superficial portion has fibers that extend down and back and fit into the angle and bottom half of the lateral surface of the ramus of the mandible. The second part, the deep portion, has fibers that go down and forward and fit into the top half of the ramus and the lateral surface of the coronoid process of the mandible. The masseter lifts the mandible and assists in protracting it. The nerve comes from the mandibular nerve. The name for this muscle means the chewer muscle.

Although the tongue may seem to be floating freely in the floor of the mouth, it is actually anchored in all directions by the four extrinsic muscle sets, which work together to move the tongue in virtually any direction. The movements they produce, however, are pretty coarse, and fine shape changes are the province of the intrinsic tongue muscles.

The extrinsic muscles are arranged in four groups. (1) The genio-glossus runs from the front of the lower jaw into the tongue from tip to base. Contraction of these muscles (on either side) makes the tongue stick out as its whole foundation is pulled forward. (2) The hyo-glossus (sometimes called the geniohyoid) is a flat, strap like muscle, which passes from the side of the tongue down to one arm of the wishbone-shaped hyoid bone in the throat. Movement of these muscles pulls the sides of the tongue downward. (3) Linking the sides of the tongue to the base of the skull through the bony styloid process (cell network) are the styo-glossals. They act to pull the tongue backward and upward. (4) The palato-glossals are connected to the sides and back of the tongue and run to the rear of the palate to lift the sides of the tongue when they are contracted.