Glossary: The Axial Skeleton

alveolar process of the mandible: upper border of mandibular body that contains the lower teeth

alveolar process of the maxilla: curved, inferior margin of the maxilla that supports and anchors the upper teeth

angle of the mandible: rounded corner located at outside margin of the body and ramus junction

angle of the rib: portion of rib with greatest curvature; together, the rib angles form the most posterior extent of the thoracic cage

anterior (ventral) sacral foramen: one of the series of paired openings located on the anterior (ventral) side of the sacrum

anterior arch: anterior portion of the ring-like C1 (atlas) vertebra

anterior cranial fossa: shallowest and most anterior cranial fossa of the cranial base that extends from the frontal bone to the lesser wing of the sphenoid bone

anterior longitudinal ligament: ligament that runs the length of the vertebral column, uniting the anterior aspects of the vertebral bodies

anulus fibrosus: tough, fibrous outer portion of an intervertebral disc, which is strongly anchored to the bodies of the adjacent vertebrae

appendicular skeleton: all bones of the upper and lower limbs, plus the girdle bones that attach each limb to the axial skeleton

articular tubercle: smooth ridge located on the inferior skull, immediately anterior to the mandibular fossa

atlas: first cervical (C1) vertebra

axial skeleton: central, vertical axis of the body, including the skull, vertebral column, and thoracic cage

axis: second cervical (C2) vertebra

body of the rib: shaft portion of a rib

brain case: portion of the skull that contains and protects the brain, consisting of the eight bones that form the cranial base and rounded upper skull

calvaria: (also, skullcap) rounded top of the skull

carotid canal: zig-zag tunnel providing passage through the base of the skull for the internal carotid artery to the brain; begins anteromedial to the styloid process and terminates in the middle cranial cavity, near the posterior-lateral base of the sella turcica

cervical curve: posteriorly concave curvature of the cervical vertebral column region; a secondary curve of the vertebral column

cervical vertebrae: seven vertebrae numbered as C1–C7 that are located in the neck region of the vertebral column

clavicular notch: paired notches located on the superior-lateral sides of the sternal manubrium, for articulation with the clavicle

coccyx: small bone located at inferior end of the adult vertebral column that is formed by the fusion of four coccygeal vertebrae; also referred to as the “tailbone”

condylar process of the mandible: thickened upward projection from posterior margin of mandibular ramus

condyle: oval-shaped process located at the top of the condylar process of the mandible

coronal suture: joint that unites the frontal bone to the right and left parietal bones across the top of the skull

coronoid process of the mandible: flattened upward projection from the anterior margin of the mandibular ramus

costal cartilage: hyaline cartilage structure attached to the anterior end of each rib that provides for either direct or indirect attachment of most ribs to the sternum

costal facet: site on the lateral sides of a thoracic vertebra for articulation with the head of a rib

costal groove: shallow groove along the inferior margin of a rib that provides passage for blood vessels and a nerve

cranial cavity: interior space of the skull that houses the brain

cranium: skull

cribriform plate: small, flattened areas with numerous small openings, located to either side of the midline in the floor of the anterior cranial fossa; formed by the ethmoid bone

crista galli: small upward projection located at the midline in the floor of the anterior cranial fossa; formed by the ethmoid bone

dens: bony projection (odontoid process) that extends upward from the body of the C2 (axis) vertebra

ear ossicles: three small bones located in the middle ear cavity that serve to transmit sound vibrations to the inner ear

ethmoid air cell: one of several small, air-filled spaces located within the lateral sides of the ethmoid bone, between the orbit and upper nasal cavity

ethmoid bone: unpaired bone that forms the roof and upper, lateral walls of the nasal cavity, portions of the floor of the anterior cranial fossa and medial wall of orbit, and the upper portion of the nasal septum

external acoustic meatus: ear canal opening located on the lateral side of the skull

external occipital protuberance: small bump located at the midline on the posterior skull

facet: small, flattened area on a bone for an articulation (joint) with another bone, or for muscle attachment

facial bones: fourteen bones that support the facial structures and form the upper and lower jaws and the hard palate

false ribs: vertebrochondral ribs 8–12 whose costal cartilage either attaches indirectly to the sternum via the costal cartilage of the next higher rib or does not attach to the sternum at all

floating ribs: vertebral ribs 11–12 that do not attach to the sternum or to the costal cartilage of another rib

fontanelle: expanded area of fibrous connective tissue that separates the brain case bones of the skull prior to birth and during the first year after birth

foramen lacerum: irregular opening in the base of the skull, located inferior to the exit of carotid canal

foramen magnum: large opening in the occipital bone of the skull through which the spinal cord emerges and the vertebral arteries enter the cranium

foramen ovale of the middle cranial fossa: oval-shaped opening in the floor of the middle cranial fossa

foramen rotundum: round opening in the floor of the middle cranial fossa, located between the superior orbital fissure and foramen ovale

foramen spinosum: small opening in the floor of the middle cranial fossa, located lateral to the foramen ovale

frontal bone: unpaired bone that forms forehead, roof of orbit, and floor of anterior cranial fossa

frontal sinus: air-filled space within the frontal bone; most anterior of the paranasal sinuses

glabella: slight depression of frontal bone, located at the midline between the eyebrows

greater wings of sphenoid bone: lateral projections of the sphenoid bone that form the anterior wall of the middle cranial fossa and an area of the lateral skull

hard palate: bony structure that forms the roof of the mouth and floor of the nasal cavity, formed by the palatine process of the maxillary bones and the horizontal plate of the palatine bones

head of the rib: posterior end of a rib that articulates with the bodies of thoracic vertebrae

horizontal plate: medial extension from the palatine bone that forms the posterior quarter of the hard palate

hyoid bone: small, U-shaped bone located in upper neck that does not contact any other bone

hypoglossal canal: paired openings that pass anteriorly from the anterior-lateral margins of the foramen magnum deep to the occipital condyles

hypophyseal (pituitary) fossa: shallow depression on top of the sella turcica that houses the pituitary (hypophyseal) gland

inferior articular process: bony process that extends downward from the vertebral arch of a vertebra that articulates with the superior articular process of the next lower vertebra

inferior nasal concha: one of the paired bones that project from the lateral walls of the nasal cavity to form the largest and most inferior of the nasal conchae

infraorbital foramen: opening located on anterior skull, below the orbit

infratemporal fossa: space on lateral side of skull, below the level of the zygomatic arch and deep (medial) to the ramus of the mandible

internal acoustic meatus: opening into petrous ridge, located on the lateral wall of the posterior cranial fossa

intervertebral disc: structure located between the bodies of adjacent vertebrae that strongly joins the vertebrae; provides padding, weight bearing ability, and enables vertebral column movements

intervertebral foramen: opening located between adjacent vertebrae for exit of a spinal nerve

jugular (suprasternal) notch: shallow notch located on superior surface of sternal manubrium

jugular foramen: irregularly shaped opening located in the lateral floor of the posterior cranial cavity

kyphosis: (also, humpback or hunchback) excessive posterior curvature of the thoracic vertebral column region

lacrimal bone: paired bones that contribute to the anterior-medial wall of each orbit

lacrimal fossa: shallow depression in the anterior-medial wall of the orbit, formed by the lacrimal bone that gives rise to the nasolacrimal canal

lambdoid suture: inverted V-shaped joint that unites the occipital bone to the right and left parietal bones on the posterior skull

lamina: portion of the vertebral arch on each vertebra that extends between the transverse and spinous process

lateral pterygoid plate: paired, flattened bony projections of the sphenoid bone located on the inferior skull, lateral to the medial pterygoid plate

lateral sacral crest: paired irregular ridges running down the lateral sides of the posterior sacrum that was formed by the fusion of the transverse processes from the five sacral vertebrae

lesser wings of the sphenoid bone: lateral extensions of the sphenoid bone that form the bony lip separating the anterior and middle cranial fossae

ligamentum flavum: series of short ligaments that unite the lamina of adjacent vertebrae

lingula: small flap of bone located on the inner (medial) surface of mandibular ramus, next to the mandibular foramen

lordosis: (also, swayback) excessive anterior curvature of the lumbar vertebral column region

lumbar curve: posteriorly concave curvature of the lumbar vertebral column region; a secondary curve of the vertebral column

lumbar vertebrae: five vertebrae numbered as L1–L5 that are located in lumbar region (lower back) of the vertebral column

mandible: unpaired bone that forms the lower jaw bone; the only moveable bone of the skull

mandibular foramen: opening located on the inner (medial) surface of the mandibular ramus

mandibular fossa: oval depression located on the inferior surface of the skull

mandibular notch: large U-shaped notch located between the condylar process and coronoid process of the mandible

manubrium: expanded, superior portion of the sternum

mastoid process: large bony prominence on the inferior, lateral skull, just behind the earlobe

maxillary bone: (also, maxilla) paired bones that form the upper jaw and anterior portion of the hard palate

maxillary sinus: air-filled space located with each maxillary bone; largest of the paranasal sinuses

medial pterygoid plate: paired, flattened bony projections of the sphenoid bone located on the inferior skull medial to the lateral pterygoid plate; form the posterior portion of the nasal cavity lateral wall

median sacral crest: irregular ridge running down the midline of the posterior sacrum that was formed from the fusion of the spinous processes of the five sacral vertebrae

mental foramen: opening located on the anterior-lateral side of the mandibular body

mental protuberance: inferior margin of anterior mandible that forms the chin

middle cranial fossa: centrally located cranial fossa that extends from the lesser wings of the sphenoid bone to the petrous ridge

middle nasal concha: nasal concha formed by the ethmoid bone that is located between the superior and inferior conchae

mylohyoid line: bony ridge located along the inner (medial) surface of the mandibular body

nasal bone: paired bones that form the base of the nose

nasal cavity: opening through skull for passage of air

nasal conchae: curved bony plates that project from the lateral walls of the nasal cavity; include the superior and middle nasal conchae, which are parts of the ethmoid bone, and the independent inferior nasal conchae bone

nasal septum: flat, midline structure that divides the nasal cavity into halves, formed by the perpendicular plate of the ethmoid bone, vomer bone, and septal cartilage

nasolacrimal canal: passage for drainage of tears that extends downward from the medial-anterior orbit to the nasal cavity, terminating behind the inferior nasal conchae

neck of the rib: narrowed region of a rib, next to the rib head

notochord: rod-like structure along dorsal side of the early embryo; largely disappears during later development but does contribute to formation of the intervertebral discs

nuchal ligament: expanded portion of the supraspinous ligament within the posterior neck; interconnects the spinous processes of the cervical vertebrae and attaches to the base of the skull

nucleus pulposus: gel-like central region of an intervertebral disc; provides for padding, weight-bearing, and movement between adjacent vertebrae

occipital bone: unpaired bone that forms the posterior portions of the brain case and base of the skull

occipital condyle: paired, oval-shaped bony knobs located on the inferior skull, to either side of the foramen magnum

optic canal: opening spanning between middle cranial fossa and posterior orbit

orbit: bony socket that contains the eyeball and associated muscles

palatine bone: paired bones that form the posterior quarter of the hard palate and a small area in floor of the orbit

palatine process: medial projection from the maxilla bone that forms the anterior three quarters of the hard palate

paranasal sinuses: cavities within the skull that are connected to the conchae that serve to warm and humidify incoming air, produce mucus, and lighten the weight of the skull; consist of frontal, maxillary, sphenoidal, and ethmoidal sinuses

parietal bone: paired bones that form the upper, lateral sides of the skull

pedicle: portion of the vertebral arch that extends from the vertebral body to the transverse process

perpendicular plate of the ethmoid bone: downward, midline extension of the ethmoid bone that forms the superior portion of the nasal septum

petrous ridge: petrous portion of the temporal bone that forms a large, triangular ridge in the floor of the cranial cavity, separating the middle and posterior cranial fossae; houses the middle and inner ear structures

posterior (dorsal) sacral foramen: one of the series of paired openings located on the posterior (dorsal) side of the sacrum

posterior arch: posterior portion of the ring-like C1 (atlas) vertebra

posterior cranial fossa: deepest and most posterior cranial fossa; extends from the petrous ridge to the occipital bone

posterior longitudinal ligament: ligament that runs the length of the vertebral column, uniting the posterior sides of the vertebral bodies

primary curve: anteriorly concave curvatures of the thoracic and sacrococcygeal regions that are retained from the original fetal curvature of the vertebral column

pterion: H-shaped suture junction region that unites the frontal, parietal, temporal, and sphenoid bones on the lateral side of the skull

ramus of the mandible: vertical portion of the mandible

ribs: thin, curved bones of the chest wall

sacral canal: bony tunnel that runs through the sacrum

sacral foramina: series of paired openings for nerve exit located on both the anterior (ventral) and posterior (dorsal) aspects of the sacrum

sacral hiatus: inferior opening and termination of the sacral canal

sacral promontory: anterior lip of the base (superior end) of the sacrum

sacrococcygeal curve: anteriorly concave curvature formed by the sacrum and coccyx; a primary curve of the vertebral column

sacrum: single bone located near the inferior end of the adult vertebral column that is formed by the fusion of five sacral vertebrae; forms the posterior portion of the pelvis

sagittal suture: joint that unites the right and left parietal bones at the midline along the top of the skull

sclerotome: medial portion of a somite consisting of mesenchyme tissue that will give rise to bone, cartilage, and fibrous connective tissues

scoliosis: abnormal lateral curvature of the vertebral column

secondary curve: posteriorly concave curvatures of the cervical and lumbar regions of the vertebral column that develop after the time of birth

sella turcica: elevated area of sphenoid bone located at midline of the middle cranial fossa

septal cartilage: flat cartilage structure that forms the anterior portion of the nasal septum

skeleton: bones of the body

skull: bony structure that forms the head, face, and jaws, and protects the brain; consists of 22 bones

somite: one of the paired, repeating blocks of tissue located on either side of the notochord in the early embryo

sphenoid bone: unpaired bone that forms the central base of skull

sphenoid sinus: air-filled space located within the sphenoid bone; most posterior of the paranasal sinuses

spinous process: unpaired bony process that extends posteriorly from the vertebral arch of a vertebra

squamous suture: joint that unites the parietal bone to the squamous portion of the temporal bone on the lateral side of the skull

sternal angle: junction line between manubrium and body of the sternum and the site for attachment of the second rib to the sternum

sternum: flattened bone located at the center of the anterior chest

styloid process: downward projecting, elongated bony process located on the inferior aspect of the skull

stylomastoid foramen: opening located on inferior skull, between the styloid process and mastoid process

superior articular process of the sacrum: paired processes that extend upward from the sacrum to articulate (join) with the inferior articular processes from the L5 vertebra

superior articular process: bony process that extends upward from the vertebral arch of a vertebra that articulates with the inferior articular process of the next higher vertebra

superior nasal concha: smallest and most superiorly located of the nasal conchae; formed by the ethmoid bone

superior nuchal line: paired bony lines on the posterior skull that extend laterally from the external occipital protuberance

superior orbital fissure: irregularly shaped opening between the middle cranial fossa and the posterior orbit

supraorbital foramen: opening located on anterior skull, at the superior margin of the orbit

supraorbital margin: superior margin of the orbit

supraspinous ligament: ligament that interconnects the spinous processes of the thoracic and lumbar vertebrae

suture: junction line at which adjacent bones of the skull are united by fibrous connective tissue

temporal bone: paired bones that form the lateral, inferior portions of the skull, with squamous, mastoid, and petrous portions

temporal fossa: shallow space on the lateral side of the skull, above the level of the zygomatic arch

temporal process of the zygomatic bone: short extension from the zygomatic bone that forms the anterior portion of the zygomatic arch

thoracic cage: consists of 12 pairs of ribs and sternum

thoracic curve: anteriorly concave curvature of the thoracic vertebral column region; a primary curve of the vertebral column

thoracic vertebrae: twelve vertebrae numbered as T1–T12 that are located in the thoracic region (upper back) of the vertebral column

transverse foramen: opening found only in the transverse processes of cervical vertebrae

transverse process: paired bony processes that extends laterally from the vertebral arch of a vertebra

true ribs: vertebrosternal ribs 1–7 that attach via their costal cartilage directly to the sternum

tubercle of the rib: small bump on the posterior side of a rib for articulation with the transverse process of a thoracic vertebra

vertebral (spinal) canal: bony passageway within the vertebral column for the spinal cord that is formed by the series of individual vertebral foramina

vertebral arch: bony arch formed by the posterior portion of each vertebra that surrounds and protects the spinal cord

vertebral column: entire sequence of bones that extend from the skull to the tailbone

vertebral foramen: opening associated with each vertebra defined by the vertebral arch that provides passage for the spinal cord

vertebra: individual bone in the neck and back regions of the vertebral column

vomer bone: unpaired bone that forms the inferior and posterior portions of the nasal septum

xiphoid process: small process that forms the inferior tip of the sternum

zygomatic arch: elongated, free-standing arch on the lateral skull, formed anteriorly by the temporal process of the zygomatic bone and posteriorly by the zygomatic process of the temporal bone

zygomatic bone: cheekbone; paired bones that contribute to the lateral orbit and anterior zygomatic arch

zygomatic process of the temporal bone: extension from the temporal bone that forms the posterior portion of the zygomatic arch

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