malar bone

bone

[bōn] 1. the hard, rigid form of connective tissue constituting most of the skeleton of vertebrates, composed chiefly of calcium salts.2. any distinct piece of the skeleton of the body. See anatomic Table of Bones in the Appendices for regional and alphabetical listings of bones, and see color plates 1 and 2. Called also os. adj., adj bo´ny.
There are 206 separate bones in the human body. Collectively they form the skeletal system, a structure bound together by ligaments at the joints and set in motion by the muscles, which are secured to the bones by means of tendons. Bones, ligaments, muscles, and tendons are the tissues of the body responsible for supporting and moving the body.
Some bones have a chiefly protective function. An example is the skull, which encloses the brain, the back of the eyeball, and the inner ear. Some, such as the pelvis, are mainly supporting structures. Other bones, such as the jaw and the bones of the fingers, are concerned chiefly with movement. The marrow" >bone marrow in the center manufactures blood cells. The bones themselves act as a storehouse of calcium, which must be maintained at a certain level in the blood for the body's normal chemical functioning. Structure and Composition. Bone is not uniform in structure but is composed of several layers of different materials. The outermost layer, the periosteum, is a thin, tough membrane of fibrous tissue. It gives support to the tendons that secure the muscle to the bone and also serves as a protective sheath. This membrane encloses all bones completely except at the joints where there is a layer of cartilage. Beneath the periosteum lie the dense, hard layers of bone tissue called compact bone. Its composition is fibrous rather than solid and it gives bone its resiliency. Encased within these layers is the tissue that makes up most of the volume of bone, called cancellous or spongy bone because it contains little hollows like those of a sponge. The innermost portion of the bone is a hollow cavity containing marrow. Blood vessels course through every layer of bone, carrying nutritive elements, oxygen, and other products. Bone tissue also contains a large number of nerves. The basic chemical in bone, which gives bone its hardness and strength, is calcium phosphate. Development. Cartilage forms the major part of bone in the very young; this accounts for the great flexibility and resiliency of the infant skeleton. Gradually, calcium phosphate collects in the cartilage, and it becomes harder and more brittle. Some of the cartilage cells break loose, so that channels develop in the bone shaft. Blood vessels enter the channels, bearing with them small cells of connective tissue, some of which become osteoblasts, cells that form true bone. The osteoblasts enter the hardened cartilage, forming layers of hard, firm bone. Other cells, called osteoclasts, work to tear down old or excess bone structure, allowing the osteoblasts to rebuild with new bone. This renewal continues throughout life, although it slows down with age.
Cartilage formation and the subsequent replacement of cartilage by hard material is the mechanism by which bones grow in size. During the period of bone growth, cartilage grows over the hardened portion of bone. In time, this layer of cartilage hardens as calcium phosphate is added, and a fresh layer grows over it, and it too hardens. The process continues until the body reaches full growth. Long bones grow in length because of special cross-sectional layers of cartilage located near the flared ends of the bone. These harden and new cartilage is produced by the same process as previously described. Bone Disorders. fracture, a break in the bone, is the most common injury to the bone; it may be closed, with no break in the skin, or open, with penetration of the skin and exposure of portions of the broken bone. osteoporosis is excessive brittleness and porosity of bone in the aged. osteomyelitis is a bone infection similar to a boil on the skin, but much more serious because blood supply to bone is less exquisite than that to other body organs and bone metabolizes more slowly, so that the infection can destroy the bone and invade other body tissues. osteomalacia is the term used for rickets when it occurs in adults. In these diseases there is softening of the bones, due to inadequate concentration of calcium or phosphorus in the body. The usual cause is deficiency of vitamin D, which is required for utilization of calcium and phosphorus by the body. In osteitis fibrosa cystica, bone is replaced by fibrous tissue because of abnormal calcium metabolism. The condition usually is due to overactivity of the parathyroid glands. osteoma refers to abnormal new growth, either benign or malignant, of the tissue of the bones. Although it is not common, it may occur in any of the bones of the body, and at any age.alveolar bone the thin layer of bone making up the bony processes of the maxilla and mandible, surrounding and containing the teeth; it is pierced by many small blood vessels, lymphatic vessels, and nerves.ankle bone talus.brittle b's osteogenesis imperfecta.bundle bone lamina dura.cancellated bone (cancellous bone) bone composed of thin intersecting lamellae, usually found internal to compact bone.cartilage bone bone developing within cartilage, ossification taking place within a cartilage model, as opposed to membranous bone.cheek bone zygomatic bone.collar bone clavicle.compact bone bone substance that is dense and hard.cortical bone the compact bone of the shaft of a bone that surrounds the marrow cavity.cranial b's the bones that constitute the cranium, including the occipital, sphenoid, temporal, parietal, frontal, ethmoid, lacrimal, and nasal bones, the inferior nasal concha, and the vomer. Some authorities also include the maxilla, zygomatic bone, and palatine bone. See anatomic Table of Bones in the Appendices.ethmoid bone the sievelike bone that forms a roof for the nasal fossae and part of the floor of the anterior cranial fossa. See anatomic Table of Bones in the Appendices.facial b's the bones that form the skeleton of the face, including the hyoid, palatine, and zygomatic bones, the mandible, and the maxilla. Some authorities include the lacrimal bones, nasal bones, inferior nasal concha, and vomer and exclude the hyoid bone. See anatomic Table of Bones in the Appendices.flat bone one whose thickness is slight, sometimes consisting of only a thin layer of compact bone, or of two layers with intervening cancellous bone and marrow; usually curved rather than flat.frontal bone the bone at the anterior part of the skull. See anatomic Table of Bones in the Appendices.heel bone calcaneus.hip bone the ilium, ischium, and pubis as a unit. See anatomic Table of Bones in the Appendices.hyoid bone a horseshoe-shaped bone at the base of the tongue. See anatomic Table of Bones in the Appendices. Called also lingual bone.incisive bone the portion of the maxilla bearing the incisors; developmentally, it is the premaxilla, which in humans later fuses with the maxilla, but in most other vertebrates persists as a separate bone.innominate bone hip bone.jaw bone either the mandible (lower jaw) or the maxilla (upper jaw). See anatomic Table of Bones in the Appendices.jugal bone zygomatic bone.lingual bone hyoid bone.long bone one whose length far exceeds its breadth and thickness.malar bone zygomatic bone.marble b's osteopetrosis.mastoid bone part of temporal bone" >mastoid part of temporal bone.membrane bone (membranous bone) bone that develops within a connective tissue membrane, in contrast to cartilage bone.occipital bone the bone constituting the back and part of the base of the skull. See anatomic Table of Bones in the Appendices.parietal bone one of two bones forming the sides and roof of the cranium. See anatomic Table of Bones in the Appendices.pelvic bone hip bone.petrous bone part of temporal bone" >petrous part of temporal bone.pneumatic bone bone that contains air-filled spaces.premaxillary bone premaxilla.pterygoid bone pterygoid process.rider's bone localized ossification sometimes seen on the inner aspect of the lower end of the tendon of the adductor muscle of the thigh in horseback riders.shin bone tibia.short bone one of approximately equal length, width, and thickness.solid bone compact bone.spongy bone cancellous bone.squamous bone part of temporal bone" >squamous part of temporal bone.sutural bone any of the variable and irregularly shaped bones in the sutures between the bones of the skull. Called also wormian bone.temporal bone one of two bones forming part of the lateral and inferior surfaces of the skull and containing the organs of hearing. See anatomic Table of Bones in the Appendices.thigh bone femur.turbinate bone a nasal concha.tympanic bone part of temporal bone" >tympanic part of temporal bone.wormian bone sutural bone.zygomatic bone the quadrilateral bone that forms a cheek. See anatomic Table of Bones in the Appendices.

zy·go·mat·ic bone

[TA] a quadrilateral bone that forms the prominence of the cheek, the lateral wall and margin of the orbit, and the anterior two thirds of the zygomatic arch; it articulates with the frontal, sphenoid, temporal, and maxillary bones. Synonym(s): os zygomaticum [TA], cheek bone (1) , jugal bone, mala (2) , malar bone, os malare, yoke bone, zygoma (1)

malar bone

n. See zygomatic bone.

zy·go·mat·ic bone

(zī'gō-mat'ik bōn) [TA] A quadrilateral bone that forms the prominence of the cheek; it articulates with the frontal, sphenoid, temporal, and maxillary bones.
Synonym(s): os zygomaticum [TA] , jugal bone, mala (2) , malar bone, zygoma (1) .

malar bone

See ZYGOMA.

orbit

A rigid bony cavity in the skull which contains an eyeball, orbital fat, the extraocular muscles, the optic nerve, nerves and blood vessels, lacrimal system and fibrous tissue of various kinds. This packing serves to keep the eyeball reasonably well fixed in place as it rotates. The orbital cavity has the approximate form of a pyramid. The walls of the orbital cavity are formed by seven bones. The medial wall of the orbit consists of: (1) the frontal process of the maxilla (maxillary); (2) the lacrimal bone; (3) the lamina papyracea of the ethmoid; and (4) a small part of the body of the sphenoid. The floor of the orbit consists of: (1) the orbital plate of the maxilla; (2) the orbital surface of the zygomatic (malar) bone and (3) the orbital process of the palatine bone. The lateral wall of the orbit consists of (1) the orbital surface of the greater wing of the sphenoid, and (2) the orbital surface of the zygomatic. The roof of the orbit is made up mainly by the frontal bone and behind this by the lesser wing of the sphenoid. The orbit is lined with a membrane of tissue called the periorbita (or orbital periosteum) which extends to the orbital margin (anterior rim of the orbit) where it becomes continuous with the periosteum covering the facial bones. The periorbita is loosely attached to the bones except at sutures, foramina and the orbital margin where it is firmly attached. The bones are much thicker at the margin (rim) than they are along the walls of the orbital cavity. There are many apertures and gaps in the orbit through which blood vessels and nerves pass (see Table O4). See orbital axis; optic canal; inferior orbital fissure; superior orbital fissure; orbital fracture; cavernous haemangioma; lamina papyracea.

Table O3 Bones forming the walls of the orbit
roof	medial wall
1. frontal	1. maxilla
2. lesser wing of sphenoid	2. lacrimal
	3. ethmoid
	4. sphenoid
floor	lateral wall
1. maxilla	1. greater wing of sphenoid
2. zygomatic
3. palatine	2. zygomatic

Table O4 Orbital apertures
aperture	location	contents
optic canal	at the apex (in lesser sphenoid)	optic nerve ophthalmic artery sympathetic nerve fibres
superior orbital fissure	at the apex (gap between greater and lesser sphenoid)	III, IV, V, VI nerves sympathetic nerve fibres ophthalmic vein recurrent lacrimal artery
inferior orbital fissure	between lateral wall and posterior part of the floor	infraorbital nerve zygomatic nerve branch of inferior ophthalmic vein nerve fibres from the pterygopalatine (sphenopalatine) ganglion to orbital periosteum
ethmoidal foramina (anterior and post.)	medial wall (frontal/ethmoidal suture)	ethmoidal vessels ethmoidal nerve/external nasal nerve
zygomatic foramen	lateral wall	zygomatic nerve and vessels
nasolacrimal canal	medial wall (maxilla/lacrimal)	nasolacrimal duct

zy·go·mat·ic bone

(zī'gō-mat'ik bōn) [TA] Quadrilateral bone that forms prominence of cheek, lateral wall and margin of orbit, and anterior two thirds of zygomatic arch; it articulates with the frontal, sphenoid, temporal, and maxillary bones.
Synonym(s): cheek bone (1) , mala (2) , malar bone, zygoma (1) .

malar bone

malar bone

malar bone

malar bone

malar bone

bone

zy·go·mat·ic bone

malar bone

zy·go·mat·ic bone

malar bone

orbit

zy·go·mat·ic bone

malar bone

Synonyms for malar bone

noun the arch of bone beneath the eye that forms the prominence of the cheek

Synonyms

Related Words