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a composite bone formed by the fusion during maturation of five sacral vertebrae that were separate at birth. The sacrum forms the back of the pelvis.
1. Osseous tissue, a specialized form of dense connective tissue consisting of bone cells (osteocytes) embedded in a nonliving matrix. Bone matrix is made of calcium carbonate, calcium phosphate, and collagen fibers. Synonym: os.
2. A unit of the skeleton; the human skeleton has 206 bones. Bones surround and protect some vital organs, and give points of attachment for the muscles, serving as levers and making movement possible. In the embryo, the bones of the skull are first made of fibrous connective tissue, which is gradually replaced by bone matrix. The remainder of the skeleton is first made of hyaline cartilage, which is also replaced by bone matrix, beginning during the third month of gestation. The outer surface of a bone is compact bone, and the inner more porous portion is cancellous (spongy) bone. The shafts of long bones are made of compact bone that surrounds a marrow canal. Compact bone is made of haversian systems, which are precise arrangements of osteocytes, blood vessels, and lymphatics within the bony matrix. All of these contribute to the maintenance and repair of bone. The periosteum is the fibrous connective tissue membrane that covers a bone. It has blood vessels that enter the bone, and it provides a site of attachment for tendons and ligaments. Bones are classified according to shape as long, short, flat, or irregular. In the elderly, esp. women, osteoporosis may develop, a condition in which bones become brittle and break easily. See: illustration; skeleton for names of principal bones
The bony tissue or process of the maxilla or mandible that supports the teeth.Synonym: alveolar process
The basilar process of the occipital bone.
Bone that is abnormally fragile, as in osteogenesis imperfecta.
A spongy bone in which the matrix forms connecting bars and plates, partially enclosing many intercommunicating spaces filled with bone marrow. Synonym: spongy bone
One of the eight wrist bones, which are aligned in two rows. The proximal row contains (from the thumb to the little finger) the scaphoid, lunate, triquetral, and pisiform bones. The distal row contains (from thumb to little finger) the trapezium, trapezoid, capitate, and hamate bones.
A bone formed by endochondral ossification developing from the primary centers of bone formation. Synonym: endochondral bone
cavalry boneRider's bone.
The hard, dense bone made of haversian systems that forms the surface layer of all bones and the shafts of long bones, in contrast to spongy bone that forms the bulk of the short, flat, and irregular bones and the ends of long bones.
A bone that forms a part of the medial portion of the acetabulum during fetal development. It subsequently fuses with the pubis.
A bone of the skull or brain case.
The outer bone of the instep bones of the foot that articulates posteriorly with the calcaneus and anteriorly with the fourth and fifth metatarsals.
One of the bones of the internal, middle, and external tarsus.
dermal boneMembrane bone.
One of the ossicles of the tympanic cavity: the malleus, incus, and stapes.See: ear for illus.
endochondral boneCartilage bone.
A complex thin-walled bone, roughly cuboidal in shape, located in the middle of the skull above the nasal cavities and below the anterior fossa of the cranial cavity. Its flat upper surface is the cribriform plate, which forms much of the roof of the nasal cavities; its upper surface has a midline bony keel that projects up into the cranial cavity and on both sides of which are perforated valleys through which the olfactory nerves project up from the olfactory epithelium. In the midline under the cribriform plate is a mirror-image (to the crista galli) keel, the perpendicular plate, which projects down between the nasal cavities as part of the bony nasal septum. The right and left sides of the ethmoid bone are the ethmoidal labyrinths, composed of ethmoidal air cells; the inner surfaces of the labyrinths form the middle nasal conchae, while the lateral surfaces form the orbital plates, which are part of the mosaic of bones that form the inner walls of the orbits.
The forehead bone.
A colloquial term for the groove along the inner back side of the elbow (behind and underneath the medial epicondyle of the humerus) in which the ulnar nerve runs. Pressure on the groove compresses the ulnar nerve, producing a tingling discomfort on the inside of the forearm as well as the 4th and 5th fingers.
greater multangular bone
The first or outermost of the distal row of carpal bones. Synonym: trapezium
The most medial wrist (carpal) bone in the distal row. It has a hooked process on its palmar side. The hamate articulates with the 4th and 5th metacarpals. Synonym: hamatum; os hamatum; unciform bone
hip boneInnominate bone.
The horseshoe-shaped bone at the base of the tongue. It is mobile and its ends hang by the stylohyoid ligaments from the styloid process on each side of the base of the skull. The hyoid bone is suspended by many muscles (the hyoid muscles): the suprahyoid muscles (geniohyoid, mylohyoid, digastric, and hyoglossus) attach the hyoid bone to the mandible and the floor of the mouth; the infrahyoid muscles (omohyoid, sternohyoid, and thyrohyoid) attach it to the larynx and the thoracic cage. The hyoid bone anchors and moves with the jaw, tongue, pharynx, and larynx.See: illustration
The part of the maxilla bearing the incisor teeth.
The hip bone or os coxae, composed of the ilium, ischium, and pubis. It is united with the sacrum and coccyx by ligaments to form the pelvis. Synonym: pelvic bone; os coxae.
The squamous portion of the occipital bone.
The alveolar bone between the roots of multirooted teeth.
intramembraneous boneMembrane bone.
ivory boneMarble bone.
A thin, irregularly shaped bone on the medial side of the orbit.
lesser multangular bone
The second in distal row of carpal bones. Synonym: trapezoid bone
lunate boneSemilunar bone.
A four-pointed bone on each side of the face, uniting the frontal and superior maxillary bones with the zygomatic process of the temporal bone. Synonym: cheekbone; zygoma; zygomatic bone
An abnormally calcified bone with a spotted appearance on a radiograph. Synonym: ivory boneSee: osteopetrosis
Any of the bones of the metatarsus.See: foot for illus.
Bone formed within embryonic fibrous connective tissue, in which fibroblasts differentiate into osteoblasts. Such bone is formed without a cartilage model and includes the bones of the face and cranium. Synonym: dermal bone; intramembraneous bone
Bone appearing as small pieces fitted together, characteristic of Paget's disease.
Either of the two small bones forming the bridge of the nose.
The bone that forms the lower, posterior skull; it articulates with the parietal and temporal bones anteriorly, and the atlas inferiorly.
The rounded end of the long process of the incus, a middle ear ossicle. It probably represents a secondary ossification center in the long or lenticular process.
palate bonePalatine bone.
One of the bones forming the posterior part of the hard palate and lateral nasal wall between the interior pterygoid plate of the sphenoid bone and maxilla. Synonym: palate bone
One of two bones that together form the posterior roof and sides of the skull.
pelvic boneInnominate bone.
Bone formed beneath the perichondrium.
Bone formed by osteoblasts of the periosteum.
ping pong bone
A thin shell of osseous tissue covering a giant-cell sarcoma in a bone.
The lower anterior part of the innominate bone. It is a separate bone at birth; it begins to fuse with the ischium by age 8, and it is fully fused with the ischium and ilium by 16-18 years of age. Synonym: os pubis
Any bone that develops within cartilage.
Ossification of the distal end of the adductor muscles of the thigh, as may be seen in horseback riders. Synonym: cavalry bone
The largest carpal bone in the first row of wristbones. It is on the thumb side of the hand and articulates directly with the radius.Synonym: os scaphoideum
Crescent-shaped bone of the carpus.Synonym: lunate bone
A type of short bone occurring in the hands and feet and embedded in tendons or joint capsules.
Soemmering's boneSee: Soemmering's bone
The large bone at the base of the skull that has the ethmoid bone in front of it, the occipital bone behind it, and the parietal and temporal bones at the sides. It is shaped like a large moth. Its two broad, curved wings form the front walls of the middle cranial fossae, and its two “tails, ” the pterygoid processes, which hang in front of the neurocranium in the pterygoid fossa behind the facial skeleton. Between the wings, in the center of the body of the sphenoid bone, there is a deep, concave pocket (the sella turcica), in which the pituitary gland lies.
spongy boneCancellous bone.
The upper anterior portion of temporal bone.
sutural boneWormian bone.
A flat bone, or one with two compact bone portions enclosing a center of spongy bone.
One of the seven bones of the ankle, hind-foot, and midfoot, consisting of the talus, calcaneus, navicular, cuboid, and three cuneiform bones.
A bone on both sides of the skull at its base. It is composed of squamous, mastoid, and petrous portions, the latter enclosing the receptors for hearing and equilibrium.Synonym: os temporale See: Arnold's canal; mastoid; petrosa; styloid process
The second bone in the distal row of carpal bones. It lies between the trapezium and capitate bones.
The third carpal bone in the proximal row, enumerated from the radial side. Synonym: triquetrum
The hamate bone, the hook-shaped bone on the ulnar side of the distal row of the carpus. Synonym: os hamatum
One of the small, irregular bones found along the cranial sutures.Synonym: sutural bone
Embryonic or rapidly growing bone characterized microscopically by a prominent fibrous matrix.
The cheekbone; the bone on either side of the face below the eye. Synonym: malar boneillustration