Axial Skeleton: Bones, Landmarks, and Terminology

Axial Skeleton

The axial skeleton forms the central axis of the human body and includes the skull, vertebral column, and thoracic cage. Understanding the bones and their landmarks is essential for identifying anatomical structures and their functions.

Cranial Bones (on Skull)

The cranial bones protect the brain and provide attachment points for head and neck muscles. Key bony landmarks are associated with each bone.

• Frontal bone

• Parietal bones

• Occipital bone

  • Foramen magnum: Large opening for the spinal cord

  • Occipital condyles: Articulate with the first cervical vertebra (atlas)

• Temporal bones

  • Styloid process: Slender pointed piece of bone below the ear

  • Mastoid process: Bony prominence behind the ear

  • Zygomatic process: Part of the cheekbone

  • Jugular foramen: Passage for the jugular vein

  • Carotid canal: Passage for the carotid artery

  • External acoustic meatus: Ear canal opening

• Ethmoid bone

  • Crista galli: Vertical projection for attachment of brain membranes

• Sphenoid bone

  • Sella turcica: Saddle-shaped depression for the pituitary gland

  • Optic canal: Passage for the optic nerve

• Sutures

  • Squamous suture: Between parietal and temporal bones

  • Coronal suture: Between frontal and parietal bones

  • Sagittal suture: Between the two parietal bones

  • Lambdoid suture: Between parietal and occipital bones

Facial Bones (on Skull)

Facial bones form the structure of the face and provide cavities for the sense organs.

• Mandible

• Maxilla

• Nasal

• Vomer

• Palatine

• Zygomatic

• Lacrimal

Thoracic Cage

The thoracic cage protects vital organs such as the heart and lungs and supports the shoulder girdles and upper limbs.

• Sternum (manubrium, body, xiphoid process)

• Ribs

Vertebral Column

The vertebral column supports the body, protects the spinal cord, and provides attachment points for ribs and muscles.

• Cervical Vertebrae

  • Atlas or C1: Supports the skull, allows nodding motion

  • Axis or C2: Contains the dens, allows rotation of the head

  • All others (C3–C7): Typical cervical vertebrae; identify transverse foramen on all

• Thoracic vertebrae

• Lumbar vertebrae

• Sacrum

  • Sacral foramina: Openings for nerves and blood vessels

• Coccyx

• Markings of all vertebrae in cervical, thoracic, and lumbar regions:

  • Vertebral body: Main weight-bearing portion

  • Spinous process: Posterior projection for muscle attachment

  • Transverse process: Lateral projections for muscle/ligament attachment

  • Vertebral foramen: Opening for the spinal cord

Newborn Skull Terminology

The newborn skull contains soft spots called fontanels, which allow for growth of the brain and skull during infancy.

• Anterior fontanel

• Posterior fontanel

• Anterolateral (sphenoidal) fontanel

• Posterolateral (mastoidal) fontanel

• Squamous suture

• Coronal suture

• Sagittal suture

• Lambdoid suture

Vocabulary: Bony Landmarks

Understanding the terminology for bony landmarks is essential for describing bone features and their functions.

Landmarks of Articulation

• Condyle: Smooth, rounded knob

• Facet: Smooth, flat, slightly concave or convex articular surface

• Head: Prominent expanded end of a bone, sometimes rounded

Elevated Landmarks

• Process: Any bony prominence

• Spine: Sharp, slender, or narrow process

• Crest: Narrow ridge

• Line: Slightly raised, elongated ridge

• Tuberosity: Rough surface

• Tubercle: Small, rounded process

• Trochanter: Massive processes unique to the femur

• Epicondyle: Projection superior to a condyle

Depressions or Flat Surfaces

• Alveolus: Pit or socket

• Fossa: Shallow, broad, or elongated basin

• Fovea: Small pit

• Sulcus: Groove for a tendon, nerve, or blood vessel

Spaces or Openings

• Foramen: Hole through a bone, usually round

• Fissure: Slit through a bone

• Meatus or canal: Tubular passage or tunnel through a bone

• Sinus: Space or cavity within a bone

Summary Table: Types of Bony Landmarks

Type	Definition	Example
Condyle	Smooth, rounded knob	Occipital condyles
Process	Any bony prominence	Mastoid process
Foramen	Hole through a bone	Foramen magnum
Fossa	Shallow, broad basin	Mandibular fossa
Sinus	Space or cavity within a bone	Maxillary sinus

Additional info:

• Fontanels in the newborn skull allow for flexibility during birth and rapid brain growth.

• The vertebral column is divided into cervical (7), thoracic (12), lumbar (5), sacral (5 fused), and coccygeal (4 fused) regions.