Bones of the Axial Skeleton

Cranial Bones of the Skull

The human skull consists of eight cranial bones that protect the brain and provide attachment sites for head and neck muscles. Each bone has distinct features and foramina for nerves and blood vessels.

• Frontal (1): Forms the forehead and upper part of the eye sockets.

  • Supraorbital foramen: Opening above each orbit for nerves and vessels.

  • Frontal sinus: Air-filled cavity within the frontal bone.

• Parietal (2): Paired bones forming the sides and roof of the cranium.

• Temporal (2): Paired bones forming the lower sides of the skull.

  • External auditory/acoustic meatus: Canal for sound transmission.

  • Zygomatic process: Articulates with the zygomatic bone.

  • Mastoid process: Attachment for neck muscles.

  • Mandibular fossa: Articulates with the mandible.

  • Jugular foramen: Passage for jugular vein.

  • Carotid foramen/canal: Passage for carotid artery.

• Occipital (1): Forms the back and base of the skull.

  • Foramen magnum: Large opening for spinal cord.

  • Occipital condyle: Articulates with the first cervical vertebra.

  • External occipital protuberance: Prominent midline bump.

• Sphenoid (1): Central bone of the skull base.

  • Greater and lesser wings: Lateral projections.

  • Superior orbital fissure: Passage for nerves to the eye.

  • Sella turcica: Houses the pituitary gland.

  • Optic foramina: Passage for optic nerves.

  • Foramen ovale: Passage for nerves.

  • Sphenoidal sinus: Air-filled cavity.

• Ethmoid (1): Located between the eyes.

  • Crista galli: Attachment for brain membranes.

  • Cribriform plates: Passage for olfactory nerves.

  • Middle nasal conchae: Increase surface area in nasal cavity.

  • Ethmoidal sinus: Air-filled cavity.

  • Perpendicular plate: Forms part of nasal septum.

Sutural Lines of the Skull

Sutures are immovable joints between skull bones. They are important for skull growth and stability.

• Coronal: Between frontal and parietal bones.

• Sagittal: Between parietal bones.

• Squamous: Between parietal and temporal bones.

• Lambdoid: Between parietal and occipital bones.

• Median palatine: Along the midline of the palate.

• Transverse palatine: Across the palate.

• Wormian (sutural) bones: Small, irregular bones within sutures.

Fontanels of the Fetal/Infant Skull

Fontanels are soft spots on the infant skull where bones have not yet fused, allowing for growth and passage through the birth canal.

• Anterior (frontal) fontanel: Largest, located at the junction of frontal and parietal bones.

• Posterior (occipital) fontanel: At the junction of parietal and occipital bones.

• Sphenoidal (anterolateral) fontanel: At the junction of frontal, parietal, temporal, and sphenoid bones.

• Mastoid (posterolateral) fontanel: At the junction of parietal, occipital, and temporal bones.

Facial Bones of the Skull

The facial skeleton consists of 14 bones that form the structure of the face, support teeth, and provide attachment for facial muscles.

• Mandible (1): Lower jawbone.

  • Mandibular condyle (condylar process): Articulates with temporal bone.

  • Coronoid process: Attachment for muscles.

  • Mental foramen: Passage for nerves and vessels.

  • Mandibular foramen: Passage for nerves.

  • Alveolar process: Supports teeth.

• Maxillary bone (2): Upper jaw.

  • Palatine process: Forms anterior hard palate.

  • Maxillary sinus: Largest paranasal sinus.

• Lacrimal bone (2): Small bones forming part of the medial orbit.

• Nasal bone (2): Form the bridge of the nose.

• Vomer bone (1): Forms part of the nasal septum.

• Inferior nasal conchae (2): Increase surface area in nasal cavity.

• Zygomatic bone (2): Cheekbones.

• Palatine bone (2): Form posterior hard palate.

• Hyoid bone (1): Located in the neck, supports tongue.

Auditory Ossicles (Middle Ear Bones)

Three pairs of tiny bones in the middle ear transmit sound vibrations.

• Malleus (hammer)

• Incus (anvil)

• Stapes (stirrup)

Vertebral Column

The vertebral column consists of 26 bones, providing support and protection for the spinal cord.

• Cervical vertebrae (7): Neck region.

  • Atlas (C1): Supports the skull.

  • Axis (C2): Allows head rotation.

  • Odontoid process (dens): Projection on axis.

• Thoracic vertebrae (12): Chest region.

• Lumbar vertebrae (5): Lower back.

• Sacrum (1): Fused vertebrae forming posterior pelvis.

• Coccyx (1): Tailbone.

• Intervertebral disk: Cartilage between vertebrae.

• Body/centrum: Main weight-bearing part.

• Spinal/vertebral foramen: Canal for spinal cord.

• Spinous process: Posterior projection.

• Transverse process: Lateral projection.

• Superior/inferior articular processes: Articulate with adjacent vertebrae.

• Intervertebral foramina: Openings for spinal nerves.

Thorax

The thorax includes the sternum and ribs, protecting vital organs and supporting breathing.

• Sternum (1): Breastbone.

  • Manubrium: Upper portion.

  • Body (gladiolus): Middle portion.

  • Xiphoid process: Inferior tip.

  • Jugular notch (suprasternal notch): Superior indentation.

  • Clavicular notch: Articulates with clavicle.

• Ribs (24): Twelve pairs.

  • Vertebrosternal (true) ribs: Directly attached to sternum.

  • Vertebrochondral ribs: Indirectly attached via cartilage.

  • False ribs: Not directly attached to sternum.

  • Floating ribs (vertebral ribs): No anterior attachment.

  • Intercostal space: Space between ribs.

  • Costal cartilage: Connects ribs to sternum.

Bones of the Appendicular Skeleton

Pectoral (Shoulder) Girdle

The pectoral girdle consists of two clavicles and two scapulae, connecting the upper limbs to the trunk.

• Clavicle (2): Collarbone.

• Scapula (2): Shoulder blade.

  • Acromion process: Articulates with clavicle.

  • Spine of scapula: Prominent ridge.

  • Coracoid process: Attachment for muscles.

  • Glenoid cavity/fossa: Articulates with humerus.

  • Lateral border (axillary border): Near armpit.

  • Medial border (vertebral border): Near spine.

Upper Extremity (Arm)

The upper limb includes the humerus, ulna, radius, carpals, metacarpals, and phalanges.

• Humerus (2): Upper arm bone.

  • Head: Articulates with scapula.

  • Greater and lesser tubercles: Muscle attachment.

  • Intertubercular groove/sulcus: Passage for tendon.

  • Surgical neck: Common fracture site.

  • Deltoid tuberosity: Attachment for deltoid muscle.

  • Trochlea: Articulates with ulna.

  • Capitulum: Articulates with radius.

  • Coronoid, olecranon, radial fossae: Depressions for forearm bones.

• Ulna (2): Medial forearm bone.

  • Trochlear notch (semilunar notch): Articulates with humerus.

  • Radial notch: Articulates with radius.

  • Coronoid and olecranon processes: Muscle attachment.

  • Styloid process: Distal projection.

  • Head: Distal end.

• Radius (2): Lateral forearm bone.

  • Head: Proximal end.

  • Radial tuberosity: Muscle attachment.

  • Ulnar notch: Articulates with ulna.

  • Styloid process: Distal projection.

• Carpals (16): Wrist bones.

  • Scaphoid (navicular), lunate, triquetrum (triangular), pisiform, hamate, capitate, trapezoid, trapezium: Eight bones per wrist.

• Metacarpals (10): Palm bones.

• Phalanges (28): Finger bones.

  • Proximal, middle, distal phalanx: Three per finger (two in thumb).

Hip or Pelvic Girdle

The pelvic girdle consists of two coxal bones, each formed by the fusion of ilium, ischium, and pubis.

• Ilium: Largest part.

  • Iliac crest: Superior border.

  • Sacroiliac joint: Articulates with sacrum.

  • Greater sciatic notch: Passage for sciatic nerve.

  • Auricular surface: Articulates with sacrum.

• Ischium: Inferior, posterior part.

  • Ischial tuberosity: Supports weight when sitting.

  • Lesser sciatic notch: Passage for nerves.

  • Ischial spine: Projection for ligament attachment.

• Pubis: Anterior part.

  • Obturator foramen: Large opening for nerves and vessels.

  • Symphysis pubis: Cartilaginous joint between pubic bones.

  • Acetabulum: Socket for femur.

  • Pubic arch: Angle below pubic symphysis.

Lower Extremity (Leg)

The lower limb includes the femur, patella, tibia, fibula, tarsals, metatarsals, and phalanges.

• Femur (2): Thigh bone.

  • Head: Articulates with acetabulum.

  • Fovea capitis: Depression for ligament attachment.

  • Neck: Connects head to shaft.

  • Greater and lesser trochanters: Muscle attachment.

  • Gluteal tuberosity: Muscle attachment.

  • Linea aspera: Ridge for muscle attachment.

  • Patella surface: Articulates with patella.

  • Medial and lateral condyles: Articulate with tibia.

• Patella (2): Kneecap.

• Tibia (2): Medial leg bone.

  • Tibial tuberosity: Attachment for patellar ligament.

  • Fibular notch: Articulates with fibula.

  • Anterior crest/border: Sharp ridge.

  • Medial malleolus: Inner ankle projection.

• Fibula (2): Lateral leg bone.

  • Head: Proximal end.

  • Lateral malleolus: Outer ankle projection.

• Tarsals (14): Ankle bones.

  • Talus, calcaneus, navicular, cuboid, 1st, 2nd, 3rd cuneiforms (medial, intermediate, lateral): Seven per foot.

• Metatarsals (10): Foot bones.

• Phalanges (28): Toe bones.

Summary Table: Axial vs. Appendicular Skeleton

This table summarizes the main bones and their counts in each division of the skeleton.

Example: Clinical Relevance

Knowledge of bone landmarks is essential for identifying fractures, muscle attachments, and sites for injections. For example, the iliac crest is used for bone marrow biopsies, and the sternum is a landmark for CPR.

Additional info: The notes correspond to Chapters 7 and 8 of standard Anatomy & Physiology textbooks, covering the skeletal system's structure and function. The list format is typical for lab practical preparation, focusing on identification and anatomical features.