Axial Skeleton

Cranial Bones

The cranial bones form the protective case around the brain and provide attachment points for head and neck muscles. Each bone has distinct markings that serve as passageways for nerves and blood vessels or as articulation points for other bones.

• Frontal Bone: Forehead region; forms the anterior part of the cranium.

  • Parts/Markings: Sagittal suture, coronal suture, squamous suture, frontal sinus

  • Location/Description: Sutures are joints between cranial bones; frontal sinus is a cavity within the frontal bone.

• Temporal Bone: Side and base of skull; houses internal ear structures.

  • Parts/Markings: External auditory meatus, internal auditory meatus, styloid process, mastoid process, zygomatic process, mandibular fossa, carotid foramen, jugular foramen

  • Location/Description: Meatuses are openings for ear structures; processes are projections for muscle attachment; foramina are passageways for nerves and vessels.

• Occipital Bone: Posterior skull; contains foramen magnum.

  • Parts/Markings: Foramen magnum, occipital condyles

  • Location/Description: Foramen magnum is the large opening for the spinal cord; condyles articulate with the first cervical vertebra.

• Sphenoid Bone: Forms base of cranium; bat-shaped.

  • Parts/Markings: Sella turcica, optic canal, foramen ovale, foramen spinosum, foramen lacerum, superior orbital fissure, inferior orbital fissure, pterygoid processes

  • Location/Description: Sella turcica holds the pituitary gland; foramina are passageways for nerves and vessels.

• Ethmoid Bone: Located between nasal cavity and orbits.

  • Parts/Markings: Crista galli, cribriform plate, middle nasal conchae, perpendicular plate

  • Location/Description: Crista galli is an attachment for brain membranes; cribriform plate has olfactory foramina; conchae and perpendicular plate form part of the nasal cavity.

Facial Bones

Facial bones shape the face, form cavities for the sense organs, and provide openings for air and food passage.

• Nasal Bone: Forms the bridge of the nose.

• Vomer: Joins with the perpendicular plate to form the nasal septum.

• Palatine: L-shaped bone posterior to maxilla.

• Mandible: Lower jaw; only movable bone of the skull.

  • Parts/Markings: Ramus, mental foramen, coronoid process, mandibular condyle, mandibular foramen

  • Location/Description: Ramus is the vertical part; mental foramen is for nerves and vessels; condyle articulates with temporal bone; foramen is passageway for nerves.

• Maxilla: Upper jaw.

  • Parts/Markings: Palatine process, infraorbital foramen

  • Location/Description: Palatine process forms the hard palate; infraorbital foramen is for nerves and vessels.

• Zygomatic Bone: Cheekbone; projects laterally.

• Inferior Nasal Conchae: Scroll-shaped bones in the nasal cavity.

Infantile Skull - Fontanels

Fontanels are soft spots on an infant's skull that allow for growth of the brain and skull during development.

• Anterior fontanel

• Posterior fontanel

• Mastoid fontanel

• Sphenoidal fontanel

Vertebral Column

General Structure

The vertebral column supports the body, protects the spinal cord, and provides attachment points for ribs and muscles. It consists of different types of vertebrae, each with unique features.

• Cervical Vertebrae: Small with forked spinous process and transverse foramen.

  • Atlas (C1): No body; articulates with occipital condyles.

  • Axis (C2): Has dens process for rotation.

• Thoracic Vertebrae: Heart-shaped body; articulation sites for ribs.

• Lumbar Vertebrae: Kidney-shaped body; large and robust.

• Sacrum: Triangular-shaped bone; fusion of five vertebrae.

  • Parts/Markings: Median sacral crest, sacral hiatus, sacral foramina

• Coccyx: Tailbone; fusion of four vertebrae.

Thoracic Cage

Sternum and Ribs

The thoracic cage protects vital organs and supports the shoulder girdles and upper limbs. It consists of the sternum and ribs.

• Sternum: Breastbone; articulates with clavicles and ribs.

  • Parts/Markings: Manubrium, body, xiphoid process, clavicular notch, jugular notch

• Ribs: Twelve pairs; true ribs (1-7) attach directly to sternum, false ribs (8-12) do not.

  • Parts/Markings: Tubercle, neck, costal cartilage

Appendicular Skeleton

Pectoral Girdle

The pectoral girdle attaches the upper limbs to the trunk and consists of the clavicle and scapula.

• Clavicle: S-shaped bone; acts as a brace.

  • Parts/Markings: Sternal end, acromial end

• Scapula: Broad, triangular bone on posterior side of the shoulder.

  • Parts/Markings: Acromion process, coracoid process, glenoid cavity, supraspinous fossa, infraspinous fossa, subscapular fossa, spine, superior/inferior/lateral borders

Upper Limb Bones

The upper limb consists of the humerus, radius, and ulna, each with distinct markings for muscle attachment and articulation.

• Humerus: Bone of the upper arm.

  • Parts/Markings: Head, greater/lesser tubercle, deltoid tuberosity, coronoid fossa, olecranon fossa, capitulum, trochlea, medial/lateral epicondyle

• Radius: Lateral bone of forearm.

  • Parts/Markings: Head, radial tuberosity, styloid process, ulnar notch

• Ulna: Medial bone of forearm.

  • Parts/Markings: Trochlear notch, olecranon process, coronoid process, styloid process

Pelvic Girdle

The pelvic girdle attaches the lower limbs to the trunk and supports the weight of the upper body.

• Os Coxae (Hip Bone): Fusion of ilium, ischium, and pubis.

  • Parts/Markings: Acetabulum, obturator foramen, greater sciatic notch, iliac crest, anterior/posterior superior/inferior iliac spine, lesser sciatic notch, ischial tuberosity, pubic symphysis

Lower Limb Bones

The lower limb consists of the femur, patella, tibia, fibula, and bones of the foot, each with specialized features for support and movement.

• Femur: Thigh bone; largest bone in the body.

  • Parts/Markings: Head, neck, greater/lesser trochanter, intertrochanteric line, linea aspera, medial/lateral condyle, medial/lateral epicondyle

• Patella: Kneecap; protects the knee joint.

• Tibia: Medial bone of leg.

  • Parts/Markings: Medial/lateral condyle, tibial tuberosity, medial malleolus

• Fibula: Lateral bone of leg.

  • Parts/Markings: Head, lateral malleolus

• Foot Bones: Tarsals (7), metatarsals (5), phalanges (14)

  • Calcaneus: Largest tarsal bone; forms the heel.

Key Tables

The following tables summarize the main bones, their markings, and locations/descriptions for identification.

Additional info:

• Fontanels allow for flexibility and growth of the infant skull during birth and early development.

• Foramina in cranial and facial bones serve as passageways for nerves and blood vessels, critical for sensory and motor functions.

• Articulation points are essential for joint movement and stability.