Skeletal System: Bones and Structures of the Human Body

Cranial Bones

Overview of 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 anatomical features and functions.

• Occipital bone: Contains the occipital condyles, foramen magnum (passage for spinal cord), and external occipital protuberance.

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

• Frontal bone: Features the supraorbital foramen/notch, forms the forehead.

• Temporal bones: Includes squamous region, petrous region, external and internal acoustic meatus, zygomatic process, styloid process, mastoid process, mandibular fossa, carotid canal, and jugular foramen (between temporal and occipital bones).

• Sphenoid bone: Contains the body, greater wings, lesser wings, sella turcica, pterygoid process, foramen spinosum, foramen ovale, foramen rotundum, and foramen lacerum (between sphenoid and temporal bone).

• Ethmoid bone: Features the cribriform plate, crista galli, perpendicular plate, and middle nasal concha.

Key Terms

• Foramen: An opening or hole in a bone for passage of nerves and blood vessels.

• Process: A projection or outgrowth of bone for muscle attachment or articulation.

Facial Bones

Overview of Facial Bones

Facial bones shape the face, form cavities for the sense organs, and provide attachment for facial muscles.

• Maxilla: Contains infraorbital foramen, palatine process, incisive fossa, and inferior nasal conchae.

• Palatine bones: Form the horizontal plate of the hard palate.

• Mandible: Features the body, mental foramen, ramus, mandibular foramen, condylar process (mandibular condyle), coronoid process, and mandibular notch.

• Zygomatic bones: Include the temporal process, form the cheekbones.

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

• Nasal bones: Form the bridge of the nose.

• Vomer bone: Forms the inferior part of the nasal septum.

Sutures

Sutures are immovable joints between skull bones.

• Lambdoid suture

• Coronal suture

• Sagittal suture

• Squamous suture

Vertebrae

Structure of a Typical Vertebra

Vertebrae are the bones forming the vertebral column, protecting the spinal cord and supporting the body.

• Body: Main weight-bearing region.

• Pedicle and Lamina: Form the vertebral arch.

• Vertebral foramen: Canal for the spinal cord.

• Transverse and Spinous processes: Projections for muscle attachment.

• Articular processes: Superior and inferior, for articulation with adjacent vertebrae.

• Intervertebral foramina: Openings for spinal nerves.

Intervertebral Disks

Fibrocartilaginous pads between vertebrae that absorb shock and allow movement.

Types of Vertebrae

• Cervical vertebrae (C1-C7):

  • C1 (Atlas): No body, supports the skull.

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

• Thoracic vertebrae (T1-T12): Each has ribs attached at costal facets.

• Lumbar vertebrae (L1-L5): Large bodies, short straight projections.

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

• Coccyx: 4-5 fused vertebrae, forms the tailbone.

Sternum

Parts of the Sternum

The sternum is a flat bone forming the anterior midline of the thorax.

• Manubrium: Contains jugular notch and clavicular notches.

• Body: Main central part.

• Xiphoid process: Inferior tip, cartilaginous in youth.

Ribs

Classification of Ribs

Ribs protect the thoracic organs and aid in respiration.

• True ribs (vertebrosternal): Pairs 1-7, attach directly to sternum.

• False ribs (vertebrochondral): Pairs 8-10, attach indirectly via cartilage.

• Floating ribs (vertebral): Pairs 11-12, do not attach to sternum.

Rib Parts

• Head, neck, articular tubercle, shaft, sternal end

Bones of the Upper Appendages

Clavicle and Scapula

The clavicle and scapula form the pectoral girdle, connecting the upper limb to the trunk.

• Clavicle: Sternal end, acromial end.

• Scapula: Features include medial border, lateral border, superior border, suprascapular notch, superior angle, inferior angle, glenoid cavity, coracoid process, acromion, spine, subscapular fossa, infraspinous fossa, supraspinous fossa.

Humerus

• Head, anatomical neck, surgical neck, greater tubercle, lesser tubercle, deltoid tuberosity, capitulum, lateral epicondyle, trochlea, medial epicondyle, olecranon fossa

Radius and Ulna

• Radius: Head, neck, radial tuberosity, styloid process, ulnar notch.

• Ulna: Olecranon, trochlear notch, coronoid process, radial notch, styloid process.

Hands

Carpals, Metacarpals, and Phalanges

The hand consists of wrist bones (carpals), palm bones (metacarpals), and finger bones (phalanges).

• Carpals: Proximal row (lateral to medial): scaphoid, lunate, triquetrum, pisiform. Distal row: trapezium, trapezoid, capitate, hamate.

• Metacarpals: I (thumb) to V (pinky), base, shaft, head.

• Phalanges: Proximal, middle, distal. Thumb has only proximal and distal phalanges.

Pelvic Girdle

Hip Bones

The pelvic girdle consists of paired hip bones (ossa coxae), supporting the lower limbs and protecting pelvic organs.

• Ilium: Iliac crest, auricular surface, acetabulum, posterior superior iliac spine, posterior inferior iliac spine, anterior superior iliac spine, anterior inferior iliac spine, greater sciatic notch.

• Ischium: Ischial spine, lesser sciatic notch, ischial tuberosity.

• Pubis: Pubic symphysis, pubic tubercle.

Lower Appendages

Femur

• Head, fovea capitis, neck, greater trochanter, lesser trochanter, intertrochanteric crest, intertrochanteric line, medial condyle, lateral condyle, medial epicondyle, lateral epicondyle, intercondylar fossa, patellar surface, linea aspera

Tibia and Fibula

• Tibia: Medial condyles, lateral condyles, intercondylar eminence, tibial tuberosity, fibular notch, medial malleolus.

• Fibula: Head, lateral malleolus.

Foot

Tarsals, Metatarsals, and Phalanges

The foot consists of ankle bones (tarsals), instep bones (metatarsals), and toe bones (phalanges).

• Tarsals: Talus, calcaneus, navicular, cuboid, cuneiforms (medial, intermediate, lateral).

• Metatarsals: I-V, base, shaft, head.

• Phalanges: Proximal, middle, distal.

Bone Tissue

Microscopic Structure of Bone

Bone tissue is composed of specialized cells and a mineralized matrix, providing strength and support.

• Osteon (Haversian system): The structural unit of compact bone.

• Lamella: Concentric rings of bone matrix within an osteon.

• Lacuna: Small spaces housing osteocytes.

• Central canal: Contains blood vessels and nerves.

Example Table: Classification of Ribs

The following table summarizes the classification and characteristics of ribs:

Type	Pairs	Attachment
True ribs (vertebrosternal)	1-7	Directly to sternum
False ribs (vertebrochondral)	8-10	Indirectly via cartilage
Floating ribs (vertebral)	11-12	No sternal attachment

Additional info:

• Some anatomical terms and bone features were expanded for clarity and completeness.

• Scientific names (e.g., ossa coxae) were italicized where relevant.