jaw

jaw¹

—jawless, adj.

/jaw/, n.

1. either of two bones, the mandible or maxilla, forming the framework of the mouth.

2. the part of the face covering these bones, the mouth, or the mouth parts collectively: My jaw is swollen.

3. jaws, anything resembling a pair of jaws or evoking the concept of grasping and holding: the jaws of a gorge; the jaws of death.

4. Mach.

a. one of two or more parts, as of a machine, that grasp or hold something: the jaws of a vise.

b. any of two or more protruding parts for attaching to or meshing with similar parts.

5. Often, jaws. Also called throat. Naut. a forked piece at the end of a gaff, fitting halfway around the mast.

6. Slang.

a. idle talk; chatter.

b. impertinent talk.

v.i.

7. Slang.

a. to talk; chat; gossip.

b. to scold or use abusive language.

v.t.

8. Slang. to scold.

[1325-75; ME jawe, jowe < OF joue; orig. uncert.]

jaw²

/jaw/, Scot. and North Eng.

n.

1. a swelling wave of water; billow.

v.i.

2. (of liquid) to surge, splash, or dash forward, as in waves.

v.t.

3. to pour or splash (liquid).

[1505-15; perh. akin to JAUP]

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Either of two bones that frame the mouth: a movable lower jaw (mandible) and a fixed upper jaw (maxilla).

These hold the teeth (see tooth) and are used for biting and chewing and in speech. Vertical portions at the back of the lower jaw form hinge joints at the temples. The front of its arch thickens to form the chin. The upper jaw is attached to bones at the bridge of the nose, in the eye sockets and roof of the mouth, and the cheekbones. It contains the large maxillary sinus.

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▪ anatomy

 either of a pair of bones that form the framework of the mouth of vertebrate animals, usually containing teeth and including a movable lower jaw (mandible) and fixed upper jaw (maxilla). Jaws function by moving in opposition to each other and are used for biting, chewing, and the handling of food.

      The mandible consists of a horizontal arch, which holds the teeth and contains blood vessels and nerves. Two vertical portions (rami) form movable hinge joints on either side of the head, articulating with the glenoid cavity of the temporal bone of the skull. The rami also provide attachment for muscles important in chewing. The centre front of the arch is thickened and buttressed to form a chin, a development unique to man and some of his recent ancestors; the great apes and other animals lack chins.

      The upper jaw is firmly attached to the nasal bones at the bridge of the nose; to the frontal, lacrimal, ethmoid, and zygomatic bones within the eye socket; to the palatine and sphenoid bones in the roof of the mouth; and at the side, by an extension, to the zygomatic bone (cheekbone), with which it forms the anterior portion of the zygomatic arch. The arched lower part of the maxilla contains the upper teeth. Inside the body of the bone is the large maxillary sinus.

      In the human fetus and infant both the upper and lower jaws have two halves; these fuse at the midline a few months after birth.

      Among the invertebrates, arthropods often have modified limbs that function in jaw action. In the subphylum Chelicerata (e.g., pycnogonids, arachnids), the pincers (chelicerae) may be used as jaws and are sometimes aided by pedipalps, which are also modified appendages. In the subphylum Mandibulata (crustaceans, insects, and myriapods), the jaw limbs are the mandibles and, to some extent, the maxillae. Such limbs may be modified for other purposes, especially in insects. Horseshoe crabs (horseshoe crab) (and perhaps the extinct trilobites) can chew food with toothed projections (gnathobases) at the bases of the walking legs, but these are not considered true jaws.

      Other important examples of invertebrate jaw structures are: in rotifers, the mastax of the pharynx; in polychaete worms, the jaws of the proboscis; in brittle stars, the five triangular oral jaws; in leeches of the order Gnathobdellida, the three toothed plates in the pharynx; and in cephalopods (e.g., octopuses), strong, horny, parrotlike beaks.

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