bone
(bōn 
)
- A specialized form of dense connective tissue consisting of bone cells (osteocytes) embedded in a nonliving matrix; osseous tissue. Bone matrix is made of calcium carbonate, calcium phosphate, and collagen fibers.SYN: os..
- A unit of a skeleton. The human skeleton has 206 bones. Bones surround and protect some vital organs, give points of attachment for the muscles, and serve as levers that make 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 (the acellular part of bone), beginning during the third month of gestation.
SEE: cancellous bone; compact bone; haversian system; long bone; membrane bone; periosteum; illus.; skeleton for names of principal bones.
The outer surface of a bone is compact bone; the inner, more porous portion is cancellous (spongy) bone. Bone is covered by periosteum. The shafts of long bones are made of compact bone that surrounds a marrow cavity. Bones are classified according to shape as long, short, flat, or irregular. Older adults, esp. womem, may develop osteoporosis.
alveolar b.The bony tissue or process of the maxilla or mand ible that supports the teeth. SYN: alveolar process; cribriform plate.
basioccipital b.The basilar process of the occipital bone.
brittle b.Bone that is abnormally fragile, as in osteogenesis imperfecta.
cancellous b.A porous bone in which the matrix forms connecting bars and plates, partially enclosing many intercommunicating spaces filled with bone marrow. SYN: spongy bone.
SEE: compact bone.
carpal 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.
cartilage b.A bone formed by endochondral ossification developing from the primary centers of bone formation. SYN: endochondral bone.
compact b.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 cancellous (spongy) bone, which forms the bulk of the short, flat, and irregular bones and the ends of long bones.
SEE: cancellous bone; haversian system.
cranial b.A bone of the skull or brain case.
cuboid b.The outer bone of the instep bones of the foot that articulates posteriorly with the calcaneus and anteriorly with the fourth and fifth metatarsals.
cuneiform b.Any of the bones of the internal, middle, and external tarsus.
ear b.Any of the ossicles of the tympanic cavity: the malleus, incus, and stapes.
SEE: ear for illus.
endochondral b.Cartilage bone.
ethmoid b.A complex, thin-walled, cuboid bone 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 (the crista galli) that projects up into the cranial cavity and serves as an attachment for the cerebral falx. On both sides of the crista galli are perforated valleys through which the olfactory nerves project up from the olfactory epithelium. In the midline under the cribriform plate is the perpendicular plate (a mirror image to the crista galli), 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; and the lateral surfaces form the orbital plates, which are part of the mosaic of bones that form the inner walls of the orbits.
facial b.Any of the 14 cranial bones that make up the face: maxillae (2); nasal (2); palatine (2); inferior nasal conchae (2); mand ible (1); zygoma (2); lacrimal (2); and vomer (1).
funny b.The groove along the posteromedial 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 fourth and fifth fingers.
greater multangular b.The first or outermost of the distal row of carpal bones. SYN: trapezium.
hamate b.The most medial carpal (wrist) bone in the distal row. It has a hooked process on its palmar side. The hamate articulates with the fourth and fifth metacarpals.SYN: hamatum; os hamatum; unciform bone.
hyoid b.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 mand ible 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: illus.
incisive b.The part of the maxilla bearing the incisor teeth.
innominate b.The hip bone composed of the ilium, ischium, and pubis. It is united with the sacrum and coccyx by ligaments to form the pelvis. SYN: pelvic bone; os coxae..
intermediate cuneiform b.Mesocuneiform.
interparietal b.The squamous portion of the occipital bone.
interradicular b.The alveolar bone between the roots of multirooted teeth.
intramembraneous b.Membrane bone.
lacrimal b.A thin, irregularly shaped bone on the medial side of the eye socket.
long b.A bone with a relatively long axis, typically found in the arms and legs. It is composed of compact bone and consists of a diaphysis and an epiphysis; each end is usually articular.
marble b.An abnormally calcified bone that on a radiograph has a spotted appearance. SYN: ivory bone.
SEE: osteopetrosis.
membrane b.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.SYN: dermal bone; intramembraneous bone.
metatarsal b.Any of the bones of the metatarsus.
SEE: foot for illus.
middle cuneiform b.Mesocuneiform.
mosaic b.Bone appearing as small pieces fitted together, a characteristic of Paget disease.
nasal b.Either of the two small bones forming the bridge of the nose.
occipital b.The bone that forms the inferior aspect of the posterior skull. It articulates with the parietal and temporal bones anteriorly and with the atlas inferiorly.
palatine b.One of the bones forming the posterior part of the hard palate and lateral nasal wall between the medial pterygoid plate of the sphenoid bone and maxilla. SYN: palate bone.
parietal b.Either of two bones that form the posterior roof and sides of the skull.
perichondrial b.Bone formed beneath the perichondrium.
periosteal b.Bone formed by osteoblasts of the periosteum.
periotic b.The mastoid and petrous portions of the temporal bone.
pubic b.The anteroinferior part of the innominate bone. It is a separate bone at birth, begins to fuse with the ischium by age 8, and is fully fused with the ischium and ilium by 16 to 18.SYN: os pubis.
replacement b.Bone that develops within cartilage.
rider b.Ossification of the distal end of the adductor muscles of the thigh, as may be seen in horseback riders.
scaphoid b.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. SYN: os scaphoideum.
second cuneiform b.Mesocuneiform.
semilunar b.A crescent-shaped bone of the carpus. SYN: lunate bone.
sesamoid b.A short bone in the hand s and feet, embedded in tendons or joint capsules, e.g. the patella.
sphenoid b.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.
squamous b.The upper flat anterior portion of temporal bone.
tabular b.A flat bone, or one with two compact bone portions enclosing a center of spongy bone.
tarsal b.One of the seven bones of the ankle, hindfoot, and midfoot, consisting of the talus, calcaneus, navicular, cuboid, and three cuneiform bones.
temporal b.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. SYN: os temporale.
SEE: mastoid; petrosa; styloid process.
trapezoid b.The second bone in the distal row of carpal bones. It lies between the trapezium and capitate bones.
triquetral b.The third carpal bone in the proximal row, enumerated from the radial side. SYN: triquetrum.
wormian b.One of the small, irregular bones found along the cranial sutures. SYN: sutural bone.
woven b.Embryonic or rapidly growing bone characterized microscopically by a prominent fibrous matrix.
zygomatic b.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. SYN: cheekbone; malar bone; zygoma.