The period of contraction of the ventricles of the heart is known as: Get exclusive access to content from our 1768 First Edition with your subscription.

The surgical treatment of mandibular angle fracture.

In the posterior two-thirds of the bone the canal is situated nearer the internal surface of the mandible; and in the anterior third, nearer its external surface. Outer aspect. Horseshoe crabs (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. The mandibular canal is of large size and runs near the lower border of the bone; the mental foramen opens beneath the socket of the first deciduous molar tooth.

About the sixth week of fetal life, intramembranous ossification takes place in the membrane covering the outer surface of the ventral end of Meckel's cartilage, and each half of the bone is formed from a single center which appears, near the mental foramen. This also remains a significant element of the jaw in some primitive bony fish, such as sturgeons.[8]. Inside the body of the bone is the large maxillary sinus.

It forms the lower jaw and holds the lower teeth in place.

The angle is obtuse (175°), and the condyloid portion is nearly in line with the body. The mental nerve exits the mental foramen and supplies sensation to the lower lip. The rami also provide attachment for muscles important in chewing.

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. [8], This complex primitive pattern has, however, been simplified to various degrees in the great majority of vertebrates, as bones have either fused or vanished entirely. The coronoid process is of comparatively large size, and projects above the level of the condyle.

Jaws function by moving in opposition to each other and are used for biting, chewing, and the handling of food. With age and tooth loss, the alveolar process is absorbed so that the mandibular canal becomes nearer the superior border.

The mandible forms as a bone (ossifies) over time from a left and right piece of cartilage called Meckel's cartilages. Instead, their lower jaw is composed of a cartilagenous structure homologous with the Meckel's cartilage of other groups. The angle becomes less obtuse, owing to the separation of the jaws by the teeth; about the fourth year it is 140°. The ramus (Latin: branch) of the human mandible has four sides, two surfaces, four borders, and two processes.

Though they are called the upper jaws, the extent and functions of the maxillae include much more than serving as complements to the lower jaw, or mandible. Jaw, 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). The larger part of the skeleton of the face is formed by the maxillae.

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