Comprehensive Study Guide: Bones, Bone Markings, and the Human Skeleton

Bones: Classification and Markings

Overview of Bone Types

The human skeleton is composed of various types of bones, each classified by their shape and function. Understanding these classifications is essential for identifying bones and their roles in the body.

• Long Bones: Longer than they are wide; primarily found in the limbs (e.g., femur, humerus).

• Short Bones: Approximately equal in length and width; provide stability and support (e.g., carpals, tarsals).

• Flat Bones: Thin, flattened, and often curved; protect internal organs (e.g., skull, ribs, sternum).

• Irregular Bones: Complex shapes that do not fit other categories (e.g., vertebrae, some facial bones).

• Sesamoid Bones: Small, round bones embedded within tendons (e.g., patella).

• Wormian Bones: Extra bone pieces within the sutures of the skull (also called sutural bones).

Bone Markings

Bones have various markings that serve as sites for muscle attachment, passage of nerves and blood vessels, or articulation with other bones.

• Depressions and Cavities:

  • Foramen: Round or oval opening through a bone (e.g., foramen magnum).

  • Fossa: Shallow depression (e.g., mandibular fossa).

  • Meatus: Canal-like passageway (e.g., external auditory meatus).

  • Fissure: Narrow, slit-like opening (e.g., superior orbital fissure).

  • Sinus: Cavity within a bone, filled with air and lined with mucous membrane (e.g., frontal sinus).

• Projections for Muscle and Ligament Attachment:

  • Tuberosity: Large, rounded projection (e.g., tibial tuberosity).

  • Trochanter: Very large, blunt, irregularly shaped process (e.g., femur).

  • Crest: Narrow, prominent ridge (e.g., iliac crest).

  • Spine: Sharp, slender projection (e.g., scapular spine).

  • Epicondyle: Raised area above a condyle (e.g., medial epicondyle of humerus).

  • Line: Narrow ridge, less prominent than a crest.

• Parts of Joint Formation:

  • Condyle: Rounded articular projection (e.g., occipital condyles).

  • Facet: Smooth, nearly flat articular surface (e.g., vertebral facets).

  • Ramus: Armlike bar of bone (e.g., mandibular ramus).

  • Head: Bony expansion carried on a narrow neck (e.g., femoral head).

Axial Skeleton

Skull Bones

The skull is composed of cranial and facial bones, protecting the brain and supporting facial structures.

• Cranium (8 bones):

  • Frontal (1): Supraorbital foramina

  • Parietal (2): Sagittal suture, Coronal suture

  • Occipital (1): Lambdoidal suture, Foramen magnum, Occipital condyles, External occipital crest

  • Temporal (2): Squamous suture, Mandibular fossa, External auditory meatus, Zygomatic process, Styloid process, Mastoid process, Petrous portion

  • Sphenoid (1): Greater wing, Superior orbital fissure, Sella turcica, Pterygoid process, Clinoid processes

  • Ethmoid (1): Concha, Perpendicular plate, Cribriform plate, Crista galli

• Foramina on Inferior Cranial Surface: Foramen ovale, Foramen spinosum, Foramen lacerum, Carotid canal, Jugular foramen, Stylomastoid foramen

• Facial Bones:

  • Maxillae (2): Palatine process, Tooth socket (alveolus), Infraorbital foramen, Incisive foramen

  • Palatines (2)

  • Zygomatics (2)

  • Lacrimal (2)

  • Nasal (2)

  • Vomer (1)

  • Mandible: Ramus, Alveoli, Coronoid process, Mandibular condyle, Mental foramen, Mandibular symphysis

• Paranasal Sinuses: Frontal sinus (2), Maxillary sinus (2), Sphenoidal sinus, Ethmoid sinus

The Vertebral Column

The vertebral column supports the body and protects the spinal cord. It is divided into regions with specialized vertebrae.

• Common Features of Vertebrae: Body, Vertebral foramen, Spinous process, Superior and inferior articular processes, Transverse processes, Vertebral arch, Intervertebral foramina, Lamina, Pedicle

• Specializations:

  • Cervical (7): Atlas (C1), Axis (C2), Superior articular surface, Transverse foramen, Odontoid process (dens)

  • Thoracic (12)

  • Lumbar (5)

  • Sacrum (5 fused): Body of sacrum, Transverse lines of fusion, Median sacral crest, Posterior and anterior sacral foramina

  • Coccyx (3-5 fused)

The Bony Thorax

The bony thorax protects vital organs and supports the shoulder girdles and upper limbs.

• Sternum: Manubrium, Body, Xiphoid process

• Ribs (12 pairs):

  • Vertebrosternal (true) ribs

  • Vertebrochondral (false) ribs

  • Vertebral (floating) ribs

  • Principal parts: Head, Tubercle, Neck, Shaft, Costal groove

Appendicular Skeleton

Bones of the Upper Extremities

• Pectoral Girdle: Clavicle, Scapula (acromion process, coracoid process, glenoid cavity, spine) (Reference only)

• Upper Arm: Humerus (head, greater and lesser tubercles, surgical neck, capitulum, trochlea, lateral and medial epicondyles, olecranon fossa)

• Lower Arm:

  • Radius: Head, Radial tuberosity, Styloid process

  • Ulna: Olecranon process, Trochlear notch, Head, Styloid process

• Hand:

  • Carpus: 8 carpal bones

  • Metacarpus: 5 metacarpal bones (#1 = thumb)

  • Phalanges: Proximal, middle, distal

Bones of the Lower Extremities

• Pelvis:

  • Os Coxa (2): Ilium (iliac crest), Acetabulum (formed by ilium, pubis, ischium), Pubis (pubic symphysis), Ischium (ischial tuberosity), Obturator foramen, Sacroiliac joint

• Upper Leg: Femur (head, neck, greater and lesser trochanters, gluteal tuberosity, lateral and medial condyles), Patella

• Lower Leg:

  • Tibia: Anterior crest, Tibial tuberosity, Lateral and medial condyles, Medial malleolus

  • Fibula: Lateral malleolus, Head

• Foot:

  • Tarsus: 7 tarsal bones (notably calcaneus and talus)

  • Metatarsus: 5 metatarsal bones (#1 most medial)

  • Phalanges: Proximal, middle, distal

Table: Classification of Bones by Shape

Bone Type	Description	Examples
Long Bones	Longer than wide, shaft with two ends	Femur, Humerus
Short Bones	Cube-shaped, nearly equal in length and width	Carpals, Tarsals
Flat Bones	Thin, flattened, often curved	Sternum, Skull bones
Irregular Bones	Complex shapes	Vertebrae, Pelvic bones
Sesamoid Bones	Small, round, embedded in tendons	Patella
Wormian Bones	Small bones within cranial sutures	Sutural bones of skull

Example: Identifying Bone Markings

• Foramen magnum: Large opening at the base of the skull for passage of the spinal cord.

• Olecranon process: Prominent projection of the ulna forming the elbow.

• Acetabulum: Deep socket in the pelvis that receives the head of the femur.

Additional info:

• Bone markings are critical for understanding muscle attachments, joint movements, and the passage of neurovascular structures.

• Knowledge of bone features is essential for clinical applications such as identifying fracture sites and interpreting radiographs.