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Related to jaw movement: ginglymoarthrodial, jaw joint


1. the part of the skull of a vertebrate that frames the mouth and holds the teeth. In higher vertebrates it consists of the upper jaw (maxilla) fused to the cranium and the lower jaw (mandible)
2. the corresponding part of an invertebrate, esp an insect
3. a pair or either of a pair of hinged or sliding components of a machine or tool designed to grip an object



(1) In animals, any of various organs of different origin used to capture and break up food. Jaws vary in structure among different taxonomic groups and are formed in the course of individual development from different rudiments; that is, they are analogous organs. Jaws exist in several invertebrates, including some worms, mollusks, and arthropods.

In arthropods, modified appendages (extremities) of the head function as jaws. In organisms whose head is fused with the thorax into a cephalothorax, the extremities of the thoracic segments usually serve to capture food, and they are called maxillipeds (crustaceans, chilopods). Particularly characteristic of arthropods is the presence of a pair of upper jaws (mandibles) and two pairs (less commonly one pair) of lower jaws (maxillae). In insects, a second pair of lower jaws fuse together to form the lower lip. Chelicerata have two pairs of head appendages that perform in part the function of jaws. The chelicerae are used to capture food, while the pedipalpi, located behind them, crush it. Among the echinoderms, sea urchins possess a complex maxillary apparatus called Aristotle’s lantern.

All vertebrates are divided into two large groups: those without jaws—the Agnatha, represented by the class Cyclostomata— and those with developed jaws—the Gnathostomata, which constitute all the other classes.

In gnathostomatous vertebrates, the jaws are situated on the facial (visceral) part of the skull. In the course of evolution, they developed first in fish as a result of the transformation of one of the anterior (third) pairs of gill arches. The upper and lower elements became reduced, while the middle portions enlarged to form the primary upper jaw, or palatoquadrate cartilage, and the primary lower jaw, or Meckel’s cartilage. Cartilaginous fishes (Chondrichthyes) have only primary cartilaginous jaws, equipped with teeth derived from the placoid scales. In bony fishes, amphibians, reptiles, birds, and mammals, substituting ossifications covered with tectorial bones developed in the posterior portions of the upper and lower jaws, from which secondary jaws then developed. Beginning with the bony fishes, a secondary jaw consisting of the premaxillary and maxillary bones forms the upper jaw. With the development of the secondary jaw, whose bones are situated along the margin of the mouth, the primary upper jaw is pushed back still farther into the palatine region of the skull and in reptiles, birds, and mammals loses its teeth. In some forms, the jaws have no teeth, and they acquire a horny structure (bill).

The development of jaws was a very important stage in the evolution of vertebrates, since it enabled vertebrates to shift from passive feeding to the active seizure of prey.

(2) In humans, the jaws are the largest bones of the visceral cranium. The upper jaw (maxilla) is a paired bone and consists of two superior maxillary bones. It occupies half of the upper part of the face, and its size and configuration greatly influence the shape of the face. Each superior maxillary bone consists of the body, with external surfaces (directed toward the nasal cavity) and posterior surfaces, and four processes—nasal, alveolar, zygomatic, and palate processes. The upper part of the bone, which is in the shape of a bent plate, forms the floor of the orbit. The interior of the body forms a cavity—the maxillary sinus, or antrum of High-more—which communicates with nasal fossae through an aperture on the internal, or nasal, surface. The alveolar process, the lower margin of the upper jaw, contains eight cavities for teeth. Together with the process of the other supermaxillary bone, it forms the dental alveolar arch.

The lower jaw (mandible) consists of the unpaired inferior maxillary bone of the facial skeleton. This only mobile cranial bone develops from symmetrical left and right halves that fuse in the center and occupies the lower part of the face. It is characterized by a V shape. Two rami project upward vertically or diagonally from the body, or horizontal portion, of the lower jaw. The superior border of the body consists of the alveolar arch, hollowed into 16 cavities for teeth. The end of each ramus breaks up into two processes: the coronoid process, to which the temporal muscle is attached, and the condyloid process, which articulates with the temporal bone. The angle between the ramus and the body varies from 90° to 140°. Nerves and blood vessels pass through the upper and lower jaws to innervate and supply the teeth with blood.


Beklemishev, V. N. Osnovy sravnitel’noi anatomii bespozvonochnykh, 3rd ed., vols. 1–2. Moscow, 1964.
Shmal’gauzen, I. I. Osnovy sravnitel’noi anatomii pozvonochnykh zhivotnykh, 4th ed. Moscow, 1947.
Prives, M. G., N. K. Lysenkov, and V. I. Butkovich. Anatomiia cheloveka, 8th ed. Leningrad, 1974.



Either of two bones forming the skeleton of the mouth of vertebrates: the upper jaw or maxilla, and the lower jaw or mandible.
A notched part that permits a railroad-car axle box to move vertically.
The side of a narrow passage such as a gorge.
References in periodicals archive ?
TMD SYMPTOMS 1983 1993 2003 10y 15y 10y 15y 10y 15y Jaw tiredness 3 4 3 9 4 7 TMJ clicking 12 16 2 14 5 17 TMJ crepitation 2 0 1 4 0 4 Locking/catching 1 5 1 5 0 2 Luxation 0 1 0 0 0 0 Reduced jaw movement 2 2 1 1 1 0 capacity Pain on jaw movement 3 2 3 2 5 2 Other pain in the face/jaws 1 1 1 4 4 Table 4.
Self-care practices, for example, eating soft foods, applying heat or ice packs, and avoiding extreme jaw movements (such as wide yawning, loud singing and gum chewing) are useful in easing TMD symptoms.
It utilizes a sensor array placed around the face and attached to a computer, and it accurately measures jaw movement both qualitatively and quantitatively in several dimensions.
TMJ dysfunction is worsened by the constant jaw movement of chewing gum.
A lot of people assume that if you have any pain in your face or jaw it's due to some sort of temporomandibular joint problem, when in fact it may be due to a muscle problem or a number of disorders affecting jaw movement," says Dr.
TMD is stress-related as much as it has to do with muscle overload, where the patients display joint symptoms - such as joint pain, reduced jaw movement, clicking or popping of the temporomandibular joint.
The process is aided by jaw movement, which assists the natural movement by dislodging debris attached to the walls of the ear canal, increasing the likelihood of its expulsion.
The patient showed mild jaw movement gradually improved and also showed clinical bony union at 4 weeks postoperatively and wires were removed (Fig.
Singing a legato line can be difficult when the tongue is unable to move smoothly between various vowels and consonants, and the problem is exacerbated when there is unnecessary jaw movement.
Sam Muslin's, Face Lift Dentistry[R] was designed to preserve the tooth structure, improve jaw movement and deliver natural-looking improvements without being invasive.
TMJ disorders result from problems with the joint or the muscles that control chewing and jaw movement.
Technical data LOAD Capacity 3000 N Range 1-100 % Available load 3000/600/120 N cells EXTENSION Maximum speed 4000 mm / min Testing/return/jog 2--4000 mm / min speed Maximum stroke 600 mm Total vertical test 840 mm space PNEUMATICS Input pressure 800 kPa / 8 bar / 110 PSI Testing pressure 800 kPa / 8 bar / 110 PSI Air preparation Filtered to 5 microns (absolute) or better to remove excess particulates, oil and moisture SAFETY Gripping Low pressure during specimen loading Jaw movement Impact protection Load cell Force overload inhibit Conformity Complies with CE Directives CONTROL SYSTEM Type CRE PC Control Windows XP or VISTA running dedicated software Drive control Digital precision closed loop A.