Bones and Bony Landmarks of the Axial Skeleton: Study Guide

Bones and Bony Landmarks of the Axial Skeleton

Overview

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 bony landmarks is essential for identifying anatomical structures and their functions.

Skull Bones and Bony Landmarks

Major Bones of the Skull

• Frontal Bone: Forms the forehead and the upper part of the eye sockets.

• Parietal Bones: Paired bones forming the sides and roof of the cranium.

• Temporal Bones: Located at the sides and base of the skull; house the structures of the ears.

• Occipital Bone: Forms the back and base of the skull.

• Nasal Bone: Forms the bridge of the nose.

• Vomer: Forms part of the nasal septum.

• Ethmoid Bone: Located between the eyes; forms part of the nasal cavity and the orbital walls.

• Sphenoid Bone: Butterfly-shaped bone at the base of the skull.

• Zygomatic Bones: Cheekbones; form part of the orbit.

• Maxilla: Upper jawbone; forms part of the orbit, nose, and palate.

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

• Lacrimal Bones: Small bones forming part of the medial wall of each orbit.

• Palatine Bones: Form part of the hard palate of the mouth and the floor of the nose.

Skull Sutures

• Sagittal Suture: Joins the two parietal bones along the midline.

• Coronal Suture: Joins the frontal bone to the parietal bones.

• Squamous (Squamosal) Suture: Joins the temporal bone to the parietal bone.

• Lambdoidal Suture: Joins the occipital bone to the parietal bones.

Bony Landmarks of the Skull

• Anterior View:

  • Mental Foramen: Opening in the mandible for nerves and blood vessels.

  • Superior Orbital Fissure: Slit in the sphenoid bone for cranial nerves.

  • Inferior Orbital Fissure: Opening between sphenoid and maxilla for nerves and vessels.

  • Optic Canal: Passage for the optic nerve.

• Lateral View:

  • Coronoid Process: Attachment site for temporalis muscle on mandible.

  • Mandibular Condyle (Condylar Process): Articulates with temporal bone to form TMJ.

  • Temporomandibular Joint (TMJ): Joint between mandible and temporal bone.

  • Mastoid Process: Projection of temporal bone; attachment for neck muscles.

  • Styloid Process: Slender projection from temporal bone; attachment for ligaments and muscles.

  • External Acoustic Meatus: Canal leading to the eardrum.

• Inferior View:

  • Foramen Magnum: Large opening for spinal cord.

  • External Occipital Protuberance: Midline projection on occipital bone.

  • Jugular Foramen: Passage for jugular vein and cranial nerves.

  • Occipital Condyle: Articulates with the first cervical vertebra (atlas).

• Internal View:

  • Cribriform Plate: Part of ethmoid bone; passage for olfactory nerves.

  • Crista Galli: Vertical projection of ethmoid bone; attachment for dura mater.

  • Greater Wing of Sphenoid: Lateral extension of sphenoid bone.

  • Lesser Wing of Sphenoid: Smaller, superior extension of sphenoid bone.

  • Sella Turcica: Depression in sphenoid bone; houses pituitary gland.

Vertebral Column: Bones and Bony Landmarks

Regions and Bones of the Vertebral Column

• Cervical Vertebrae: 7 vertebrae (C1–C7); support the head and allow for its movement.

• Thoracic Vertebrae: 12 vertebrae (T1–T12); articulate with the ribs.

• Lumbar Vertebrae: 5 vertebrae (L1–L5); largest vertebrae, support lower back.

• Sacrum: 5 fused vertebrae; forms the posterior wall of the pelvis.

• Coccyx: 3–5 fused vertebrae; forms the tailbone.

Bony Landmarks of Vertebrae

• Vertebral Foramen: Opening for the spinal cord.

• Transverse Process: Lateral projections for muscle and ligament attachment.

• Spinous Process: Posterior projection; palpable along the back.

• Lamina: Part of the vertebral arch between transverse and spinous processes.

Identifying Vertebral Regions

• Cervical Vertebrae: Small body, bifid spinous process, transverse foramina.

• Thoracic Vertebrae: Larger body, long spinous process, facets for rib articulation.

• Lumbar Vertebrae: Largest body, short and blunt spinous process, no rib facets.

Thoracic Cage Bones

Components of the Thoracic Cage

• Ribs: 12 pairs; protect thoracic organs.

  • True Ribs (1–7): Directly attached to sternum via costal cartilage.

  • False Ribs (8–12): Indirectly attached or not attached to sternum.

  • Floating Ribs (11–12): Not attached to sternum.

• Clavicle: Collarbone; connects sternum to scapula.

• Sternum: Breastbone; consists of manubrium, body, and xiphoid process.

• Hyoid Bone: U-shaped bone in the neck; does not articulate with other bones.

Summary Table: Axial Skeleton Bones and Landmarks

Region	Main Bones	Bony Landmarks
Skull	Frontal, Parietal, Temporal, Occipital, Nasal, Vomer, Ethmoid, Sphenoid, Zygomatic, Maxilla, Mandible, Lacrimal, Palatine	Mental foramen, superior/inferior orbital fissure, optic canal, coronoid process, mandibular condyle, TMJ, mastoid process, styloid process, external acoustic meatus, foramen magnum, external occipital protuberance, jugular foramen, occipital condyle, cribriform plate, crista galli, greater/lesser wing of sphenoid, sella turcica
Vertebral Column	7 cervical, 12 thoracic, 5 lumbar, sacrum, coccyx	Vertebral foramen, transverse process, spinous process, lamina
Thoracic Cage	Ribs (true, false, floating), clavicle, sternum, hyoid bone	Costal cartilage, manubrium, body, xiphoid process

Additional info:

• The axial skeleton provides support and protection for the brain, spinal cord, and thoracic organs.

• Bony landmarks are essential for muscle attachment, passage of nerves and blood vessels, and articulation with other bones.

• Understanding the views (anterior, lateral, inferior, internal) is crucial for identifying specific landmarks.