Axial & Appendicular Skeleton: Bone Markings and Functions

Axial & Appendicular Skeleton Overview

Introduction

The human skeleton is divided into two major parts: the axial skeleton and the appendicular skeleton. Each part contains specific bones with unique markings and functions. Understanding these divisions and the associated bone features is essential for the study of anatomy and physiology.

• Axial skeleton: Includes the skull, vertebral column, and thoracic cage.

• Appendicular skeleton: Includes the pectoral girdle, pelvic girdle, and limbs.

• Bones are classified by shape: flat, irregular, long, short, and sesamoid.

• Bone markings serve as attachment sites, passageways for nerves and blood vessels, and articulation points.

Cranial Bones – Axial Skeleton

Main Bones and Markings

The cranial bones protect the brain and provide attachment points for head and neck muscles. Key markings are important for anatomical orientation and clinical reference.

Bone	Shape	Important Bone Markings / Areas
Parietal	Flat	Coronal, sagittal, lambdoid, & squamous sutures; sutural bones
Frontal	Flat	Supraorbital margin, frontal sinus, supraorbital foramen, external acoustic meatus, glabella, zygomatic process, orbital, nasal, mastoid process
Occipital	Flat	Foramen magnum, occipital condyle, external occipital protuberance
Temporal	Irregular	Zygomatic process, carotid canal, mastoid process, styloid process, jugular foramen, superior orbital fissure, sella turcica, lesser wing, optic canal
Ethmoid	Irregular	Crista galli, cribriform plate, cribriform foramen, perpendicular plate

Facial Bones – Axial Skeleton

Main Bones and Markings

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

Bone	Shape	Important Bone Markings / Areas
Nasal	Flat
Lacrimal	Flat	Lacrimal fossa
Zygomatic	Irregular
Inferior nasal concha	Irregular
Vomer	Irregular
Maxilla	Irregular	Palatine process, alveolar process
Mandible	Irregular	Condylar process, coronoid process, mandibular notch, body, ramus, alveolar process, mandibular foramen

Vertebral Column, Thoracic Cage – Axial Skeleton

Main Bones and Markings

The vertebral column supports the body and protects the spinal cord. The thoracic cage protects vital organs and provides attachment points for muscles.

Bone	Shape	Important Bone Markings / Areas
Vertebrae	Irregular	Vertebral foramen, transverse process, spinous process, superior & inferior articular processes, intervertebral discs
Cervical	Irregular	Atlas (C1), axis (C2), dens, transverse foramen, C2–C6 bifid spinous process
Thoracic/Lumbar	Irregular
Sternum	Flat
Coccyx	Irregular	Median sacral crest, sacral foramen, sacral canal, sacral hiatus

Pectoral Girdle & Upper Extremity – Appendicular Skeleton

Main Bones and Markings

The pectoral girdle connects the upper limb to the trunk. The bones of the upper extremity allow for a wide range of motion and manipulation.

Bone	Shape	Important Bone Markings / Areas
Clavicle	Long	Acromial end, sternal end
Scapula	Flat	Medial & lateral borders, glenoid cavity, spine, acromion, coracoid process
Humerus	Long	Head, anatomical neck, surgical neck, greater & lesser tubercles, deltoid tuberosity, capitulum, trochlea, lateral & medial epicondyles, olecranon fossa
Radius	Long	Head, radial tuberosity
Ulna	Long	Olecranon, trochlear notch, coronoid process, radial notch
Carpals	Short	Proximal row (lateral to medial): scaphoid, lunate, triquetrum, pisiform
Hand Metacarpals	Long	Distal row (lateral to medial): trapezium, trapezoid, capitate, hamate
Phalanges	Long	1-5, proximal phalanx, middle phalanx (except thumb), distal phalanx

Pelvic Girdle & Lower Extremity – Appendicular Skeleton

Main Bones and Markings

The pelvic girdle supports the weight of the upper body and protects pelvic organs. The lower extremity bones are adapted for weight-bearing and locomotion.

Bone	Shape	Important Bone Markings / Areas
Pelvic Girdle	Irregular	Acetabulum, obturator foramen, pelvic brim
Os coxa	Irregular	Iliac crest, anterior superior & inferior iliac spines, posterior superior & inferior iliac spines, greater sciatic notch
Pubis	Irregular	Pubic arch
Femur	Long	Head, neck, greater & lesser trochanters, gluteal tuberosity, medial & lateral condyles, medial & lateral epicondyles, intercondylar fossa, patellar surface
Patella	Sesamoid
Tibia	Long	Medial & lateral condyles, tibial tuberosity, medial malleolus
Fibula	Long	Head, lateral malleolus
Foot Tarsals	Short	Talus, calcaneus, navicular, medial cuneiform, intermediate cuneiform, lateral cuneiform, cuboid
Metatarsals	Long	1-5
Phalanges	Long	1-5, proximal phalanx, middle phalanx (except hallux), distal phalanx

Bone Classification and Functions

Definitions and Examples

• Flat bones: Thin, flattened, and usually curved (e.g., parietal, frontal, scapula).

• Irregular bones: Complicated shapes (e.g., vertebrae, sphenoid, ethmoid).

• Long bones: Longer than they are wide (e.g., humerus, femur, phalanges).

• Short bones: Cube-shaped (e.g., carpals, tarsals).

• Sesamoid bones: Embedded in tendons (e.g., patella).

Functions of bone markings:

• Serve as attachment points for muscles, ligaments, and tendons.

• Allow passage of nerves and blood vessels.

• Form joints and articulation surfaces.

Key Terms and Examples

Selected Bone Markings

• Foramen magnum: Large opening in the occipital bone for the spinal cord.

• Acetabulum: Socket in the pelvic bone for the femur head.

• Deltoid tuberosity: Raised area on the humerus for deltoid muscle attachment.

• Mandibular foramen: Opening in the mandible for nerves and vessels.

• Greater sciatic notch: Indentation in the ilium for sciatic nerve passage.

Comparing Axial and Appendicular Skeletons

Classification Table

Skeleton	Main Components	Function
Axial	Skull, vertebral column, thoracic cage	Protection of brain, spinal cord, and thoracic organs; support
Appendicular	Pectoral girdle, pelvic girdle, limbs	Movement, manipulation, locomotion

Additional info:

• Bone markings are often bolded in anatomical diagrams to highlight their clinical or functional importance.

• Students should be able to identify bones and markings from diagrams and models, and understand their relevance to muscle attachment and joint movement.