Anatomy of Bone Structure and Skull Bones: Osteons, Skull, and Vertebrae

Osteon (Haversian System)

Structural unit of compact bone; looks like tree rings under a microscope. Found in the shaft of long bones like the femur.

Central Canal (Haversian Canal)

Channel in the center of each osteon containing blood vessels and nerves that provide nourishment to osteocytes.

Concentric Lamellae

Rings of calcified matrix arranged around the central canal that strengthen the bone.

Interstitial Lamellae

Remnants of older osteons found between newer ones; fill gaps for structural stability.

Circumferential Lamellae

Layers of bone matrix running around the outer and inner surface of the bone; reinforce the bone wall.

Lacunae

Small cavities between lamellae that house osteocytes (bone cells).

Osteocytes

Mature bone cells that maintain the bone matrix and communicate through canaliculi.

Periosteum

Outer dense connective tissue covering bone; rich in nerves and blood vessels; attachment for tendons and ligaments.

Nutrient Foramina

Small openings that allow blood vessels and nerves to enter and exit the bone.

Perforating (Volkmann's) Canals

Canals running perpendicular to central canals; connect blood vessels and nerves between osteons.

Frontal Bone

Forehead bone forming the anterior skull and roof of the orbits.

Parietal Bone

Forms the upper sides and roof of the skull; paired bone.

Temporal Bone

Side of skull around ear region; includes mastoid and styloid processes.

Occipital Bone

Back and base of skull containing the foramen magnum.

Sphenoid Bone

Butterfly-shaped bone in the skull base that contains the sella turcica for the pituitary gland.

Ethmoid Bone

Light, spongy bone between the eyes forming part of the nasal cavity and eye orbits.

Lacrimal Bone

Small bone forming the medial wall of the orbit; contains tear ducts.

Maxilla (Maxillary Bones)

Upper jaw bones forming the hard palate and holding upper teeth.

Zygomatic Bone

Cheekbones; form lateral wall of orbit.

Nasal Bone

Small paired bones forming the bridge of the nose.

Vomer

Forms the inferior part of the nasal septum.

Inferior Nasal Conchae

Curved bones inside the nasal cavity that increase surface area for warming and filtering air.

Palatine Bone

Forms the posterior part of the hard palate and nasal cavity.

Alveolar Processes

Bony ridges that contain tooth sockets in maxilla and mandible.

Zygomatic Arch

Cheekbone bridge formed by zygomatic and temporal bones.

Occipital Condyles

Rounded projections on occipital bone that articulate with the first cervical vertebra (atlas).

Mastoid Process

Rounded projection behind ear; attachment for neck muscles.

Mandibular Fossa

Depression in temporal bone where mandible articulates to form TMJ (jaw joint).

Foramen Magnum

Large opening at skull base for passage of spinal cord.

Optic Canal (Foramen)

Passage for optic nerve from eye to brain.

External Acoustic Meatus

Ear canal leading to the eardrum.

Sella Turcica

"Turkish saddle" depression in sphenoid bone holding the pituitary gland.

Body of Mandible

Horizontal portion forming the lower jaw and chin.

Ramus of Mandible

Vertical part of mandible connecting to the skull.

Coronoid Process

Anterior projection of mandible for muscle attachment.

Condylar Process

Posterior projection that articulates with the temporal bone to form TMJ.

Anterior Fontanelle

Soft spot on top of infant skull; allows brain growth and birth flexibility.

Sphenoidal (Anterolateral) Fontanelle

Soft spot near temples.

Mastoid (Posterolateral) Fontanelle

Soft spot behind ears.

Posterior Fontanelle

Soft spot at back of infant skull; closes first.

Hyoid Bone

U-shaped bone in neck that supports tongue and muscles; not attached to any other bone.

Cervical Region

Top section of vertebral column; 7 vertebrae in the neck.

Thoracic Region

Middle section of vertebral column; 12 vertebrae that articulate with ribs.

Lumbar Region

Lower back; 5 large, weight-bearing vertebrae.

Sacral Region

5 fused vertebrae forming sacrum; part of pelvis.

Coccygeal Region

3-5 fused vertebrae forming coccyx or tailbone.

Vertebral Body

Large anterior portion that supports body weight.

Spinous Process

Posterior projection for muscle and ligament attachment.

Transverse Process

Lateral projections for muscle and rib attachment.

Vertebral Foramen

Central opening for the spinal cord.

Laminae

Flat parts between spinous and transverse processes.

Superior Articular Process

Upward projection for articulation with vertebra above.

Inferior Articular Process

Downward projection for articulation with vertebra below.

Atlas (C1)

First cervical vertebra supporting skull; allows nodding motion 'yes.'

Axis (C2)

Second cervical vertebra; contains the dens allowing rotation 'no.'

Dens (Odontoid Process)

Peg-like projection on axis fitting into atlas.

Thoracic Vertebra

Heart-shaped body; articulates with ribs via costal facets.

Lumbar Vertebra

Large and strong vertebrae of lower back.

Sacrum

Fused bone forming posterior wall of pelvis.

Sacral Canal

Continuation of vertebral canal carrying nerves.

Sacral Foramina

Openings for passage of sacral nerves and vessels.

Median Sacral Crest

Ridge on posterior sacrum formed by fused spinous processes.

Coccyx

Tailbone at bottom of spine; provides attachment for ligaments.

Ribs

12 pairs of curved bones protecting thoracic cavity.

Head of Rib

Articulates with vertebral body.

Tubercle of Rib

Bump that articulates with transverse process.

Costal Groove

Indentation on internal surface housing nerves and vessels.

Sternum

Flat bone in chest; composed of manubrium, body, xiphoid process.

Manubrium

Upper part of sternum; articulates with clavicles.

Sternal Angle

Ridge where manubrium meets body of sternum.

Body of Sternum

Middle section; ribs attach here.

Xiphoid Process

Small tip at lower sternum; landmark for CPR.

Costal Cartilage

Hyaline cartilage attaching ribs to sternum.

Clavicle

Collarbone connecting sternum and scapula.

Scapula

Shoulder blade; triangular bone on back.

Spine of Scapula

Prominent ridge on posterior scapula.

Acromion Process

Lateral extension of spine; forms shoulder tip.

Coracoid Process

Anterior projection for muscle attachment.

Supraspinous Fossa

Depression above scapular spine.

Infraspinous Fossa

Depression below scapular spine.

Subscapular Fossa

Depression on anterior surface.

Glenoid Cavity

Socket where humeral head articulates (shoulder joint).

Ilium

Superior broad region of coxal bone.

Ischium

Inferior posterior portion of pelvis.

Pubis

Anterior portion forming front of pelvis.

Iliac Crest

Curved upper ridge of ilium.

Anterior Superior Iliac Spine

Front projection of iliac crest; surface landmark.

Posterior Superior Iliac Spine

Rear projection of iliac crest.

Acetabulum

Deep socket for femoral head articulation.

Obturator Foramen

Large hole for nerves and vessels in pelvis.

Ischial Tuberosity

Rough area for hamstring attachment.

Greater Sciatic Notch

Large indentation allowing passage of sciatic nerve.

Auricular Surface

Articulation site with sacrum.

Gluteal Surface

Outer ilium surface for gluteal muscles.

Pubic Symphysis

Joint connecting the two pubic bones.

Humerus

Bone of upper arm; articulates with scapula and forearm bones.

Head of Humerus

Rounded proximal end fitting into glenoid cavity.

Greater Tubercle

Large lateral projection for muscle attachment.

Lesser Tubercle

Smaller anterior projection for muscle attachment.

Bicipital Groove

Groove for biceps tendon between tubercles.