Overview of the Human Skeletal System: Bone Classification, Structure, and Terminology

SKULL (22 Bones Total)

Cranial Bones (8)

The cranial bones form the protective case around the brain and contribute to the structure of the skull. They provide attachment points for muscles and house important foramina for nerves and blood vessels.

• Frontal (1) – Forehead; forms the front of the skull and upper eye sockets.

• Parietal (2) – Large bones forming the sides and top of the skull.

• Temporal (2) – Sides near the ears; contain ear structures.

  • Styloid process – Pointed projection for tongue and neck muscle attachment.

  • Mastoid process – Bump behind the ear; attachment for neck muscles.

  • External auditory meatus – Ear canal opening.

  • Internal auditory meatus – Passage for nerves to the inner ear.

• Occipital (1) – Back and base of the skull.

  • Foramen magnum – Large hole for spinal cord connection.

  • Occipital condyles – Rounded projections that articulate with the atlas (C1).

  • External occipital protuberance – Bump on back of skull for ligament attachment.

• Sphenoid (1) – Butterfly-shaped bone connecting many skull bones.

  • Optic foramen (canal) – Opening for optic nerve.

• Ethmoid (1) – Between the eyes; supports the nasal cavity.

  • Olfactory foramina – Tiny holes for smell (olfactory) nerves.

Facial Bones (14)

Facial bones form the structure of the face, nasal cavity, and jaw. They provide support for teeth, anchor facial muscles, and form the nasal and oral cavities.

• Maxilla (2) – Upper jaw; holds upper teeth; forms part of the nose and eye sockets.

• Zygomatic (2) – Cheekbones; connect to temporal bones.

• Mandible (1) – Lower jaw; only movable skull bone.

  • Body, ramus, angle, condyle – Form the shape and articulation.

• Nasal (2) – Bridge of the nose.

• Lacrimal (2) – Small bones near tear ducts.

• Palatine (2) – Form the back part of the hard palate (roof of mouth).

• Inferior nasal concha (2) – Curved bones inside the nose that help filter air.

• Vomer (1) – Lower part of the nasal septum.

Auditory Ossicles (6)

Tiny bones inside the ear that transmit sound vibrations.

• Malleus (2) – "Hammer"

• Incus (2) – "Anvil"

• Stapes (2) – "Stirrup"

Hyoid Bone (1)

A U-shaped "floating" bone in the neck; anchors tongue and swallowing muscles. It's the only bone that doesn't directly connect to another bone.

Joints and Features of the Skull

• Sutures – Joints where skull bones meet: Coronal (frontal/parietal), Sagittal (between parietals), Lambdoid (parietal/occipital).

• Orbit – Eye socket (frontal + zygomatic + maxilla + ethmoid).

• Temporomandibular joint (TMJ) – Jaw joint (temporal + mandible).

• Nasal septum – Divider of nasal cavity (vomer + ethmoid).

• Hard palate – Roof of mouth (maxilla + palatine).

• Anterior fontanel (fetal) – "Soft spot" where bones haven’t fused yet.

VERTEBRAL COLUMN (26 Bones Total)

The vertebral column supports the body and protects the spinal cord. It is divided into regions, each with distinct functions and features.

Regions

• Cervical vertebrae (7) – Neck; C1 (atlas) supports the skull, C2 (axis) allows head rotation.

• Thoracic vertebrae (12) – Upper/mid-back; connect to ribs.

• Lumbar vertebrae (5) – Lower back; thick for weight bearing.

• Sacrum (1, fused from 5) – Connects spine to pelvis.

• Coccyx (1, fused from 4) – Tailbone.

Features of Each Vertebra

• Body (centrum) – Weight-bearing part.

• Vertebral foramen – Opening for spinal cord.

• Spinous & transverse processes – Projections for muscle attachment.

• Intervertebral discs – Cartilage cushions between vertebrae.

THORACIC CAGE (25 Bones Total)

The thoracic cage protects the heart, lungs, and upper organs. It consists of the sternum and ribs.

• Sternum (1) – Flat breastbone in center of chest.

  • Manubrium (top), body (middle), xiphoid process (tip).

  • Jugular notch – Top dip.

  • Sternal angle – Joint between manubrium and body.

• Ribs (24 = 12 pairs)

  • True ribs (1–7) – Attach directly to sternum.

  • False ribs (8–10) – Attach indirectly via cartilage.

  • Floating ribs (11–12) – No anterior attachment.

  • Head connects to spine; costal cartilage connects front end to sternum.

PECTORAL (SHOULDER) GIRDLE (4 Bones Total)

The pectoral girdle connects arms to the trunk and allows a wide range of movement.

• Clavicles (2) – Collar bones; connect sternum to scapula.

  • Sternal end – Attaches to sternum.

  • Acromial end – Attaches to scapula.

• Scapulae (2) – Shoulder blades.

  • Spine, acromion, coracoid process – Muscle attachment sites.

  • Glenoid cavity – Socket for humerus (shoulder joint).

  • Acromioclavicular joint – Clavicle-scapula connection.

  • Infraspinous & supraspinous fossae – Muscle attachment areas.

UPPER LIMBS (60 Bones Total → 30 per Arm)

Arm and Forearm

• Humerus (2) – Upper arm; articulates with scapula and radius/ulna.

  • Head, epicondyles, trochlea, capitulum

• Radius (2) – Lateral forearm (thumb side).

  • Head, radial tuberosity, styloid process

• Ulna (2) – Medial forearm (pinky side).

  • Olecranon (elbow bump), head, styloid process

Hands

• Carpals (16 = 8 per wrist) – Wrist bones.

  • Mnemonic: "Sally Left The Party To Take Cathy Home" (Scaphoid, Lunate, Triquetrum, Pisiform, Trapezium, Trapezoid, Capitate, Hamate)

• Metacarpals (10 = 5 per hand) – Palm bones.

• Phalanges (28 = 14 per hand) – Finger bones (3 per finger, 2 per thumb).

PELVIC GIRDLE (2 Bones Total)

The pelvic girdle supports the trunk and connects the legs to the axial skeleton.

• Coxal (hip) bones (2) – Each formed by 3 fused bones:

  • Ilium (top), Ischium (bottom-back), Pubis (front).

  • Acetabulum – Deep socket for femur.

  • Iliac crest & spines – Muscle attachments.

  • Ischial tuberosity – "Sit bone."

  • Pubic symphysis – Cartilage joint between pubic bones.

  • Obturator foramen – Hole for nerves and vessels.

LOWER LIMBS (60 Bones Total → 30 per Leg)

Leg

• Femur (2) – Thigh bone; longest, strongest bone.

  • Head fits into acetabulum, greater/lesser trochanters for muscle attachment, condyles for knee joint.

• Patella (2) – Kneecap; protects knee joint.

• Tibia (2) – Shin bone; main weight-bearing bone.

  • Condyles, tibial tuberosity, medial malleolus

• Fibula (2) – Smaller lateral bone of leg.

  • Head, lateral malleolus

Feet

• Tarsals (14 = 7 per ankle) – Ankle bones.

• Metatarsals (10 = 5 per foot) – Foot bones.

• Phalanges (28 = 14 per foot) – Toe bones (3 per toe, 2 per big toe).

MICROSCOPIC BONE STRUCTURE (Osteon Model)

Compact bone is organized into structural units called osteons (Haversian systems). These units provide strength and facilitate nutrient and waste exchange.

• Osteon (Haversian system) – Structural unit of compact bone.

• Central canal – Contains blood vessels and nerves.

• Lamellae – Rings of bone matrix.

• Lacunae – Small spaces housing osteocytes (bone cells).

• Osteocytes – Maintain bone tissue.

• Perforating (Volkmann’s) canals – Side channels connecting central canals.

• Periosteum – Outer membrane of bone.

• Trabeculae – Lattice-like network in spongy bone for lightness and strength.

DIRECTIONAL TERMS

Directional terms are used to describe body position or orientation in anatomy.

Term	Meaning
Medial	Toward midline
Lateral	Away from midline
Superior	Above
Inferior	Below
Anterior (ventral)	Front
Posterior (dorsal)	Back
Proximal	Closer to trunk or point of attachment
Distal	Farther from trunk or point of attachment

BONE COUNT SUMMARY

The following table summarizes the number of bones in each major region of the adult human skeleton.

Region	Number of Bones
Skull (Cranial + Facial)	22
Auditory Ossicles	6
Hyoid	1
Vertebral Column	26
Thoracic Cage (Sternum + Ribs)	25
Pectoral Girdle	4
Upper Limbs	60
Pelvic Girdle	2
Lower Limbs	60
TOTAL	206 Bones

Additional info:

• The adult human skeleton typically consists of 206 bones, though this number can vary slightly due to anatomical variations such as extra vertebrae or ribs.

• Bone structure and terminology are foundational for understanding movement, protection, and support in the human body.