The mandible (Figure 3.15) forms the lower jaw and is the strongest and largest facial bone. It is the only mov-able bone in the skull (excluding the auditory ossicles, which vibrate with sound). It is divided into the hori-zontal portion (body) and the ascending portion (ra-mus) (plural, rami). The point where the body and theramus meet is the angle. The posterior projection of the ramus (condylar process) articulates with the mandibular fossa and articular tubercle of the tempo-ral bone to form the temporomandibular joint. The condylar process has a head and a neck. The anterior projection (coronoid process) is the location where the temporalis muscle inserts. This is the muscle that can be felt or seen moving in your temples when you move your jaw. The dent between the two processes is known as the mandibular notch. On the superior sur-face of the body, the alveolar processes with the alve-oli(depressions) give attachment to the teeth of thelower jaw. Nerves and blood vessels pass through the bone through special foramen. The mental foramen is located inferior to the location of the premolars, and the mandibular foramen is located on the inner sur-face of the ramus. Dentists often anesthetize the nerves passing through these foramen.
The hyoid bone, a small, U-shaped bone located in front of the neck, is held in place by ligaments. The hyoid bone serves as a base for the attachment of sev-eral muscles that are concerned with the movement of the tongue and larynx.
The bones in an infant’s skull are not fused. In-stead, there are fibrous areas between the bones called fontanels (see Figure 3.16). The largest is the anterior fontanel, which lies where the frontal and the two parietal bones meet. There is a posteriorfontanel where the occipital and parietal bonesmeet. In addition, there are fontanels in the side of the skull, along the squamosal and lambdoid sutures, called sphenoidal or anterolateral fontanels and mastoid or posterolateral fontanels. The sphe-noidal, mastoid, and posterior fontanels fuse a month or two after birth, while the anterior fontanel fuses at about age two. The fontanels allow the skull to modify its shape as it passes through the pelvic outlet of the mother, without damage to the brain.