Bones and Bone Features

Axial Skeleton

The axial skeleton forms the central axis of the body and includes the skull, vertebral column, and thoracic cage. It provides support and protection for the brain, spinal cord, and thoracic organs.

A. Sutures

• Coronal suture: Separates the frontal bone from the parietal bones.

• Sagittal suture: Divides the left and right parietal bones.

• Lambdoid suture: Separates the occipital bone from the parietal bones.

• Squamous suture: Separates the temporal bone from the parietal bone.

• Occipitomastoid suture: Connects the occipital bone to the mastoid portion of the temporal bone.

B. Cranial Bones (8 total)

• Frontal: Forms the forehead and the roof of the orbits.

• Parietal (2): Form the sides and roof of the cranial cavity.

• Occipital: Forms the posterior part of the skull and base of the cranium.

  • External occipital protuberance: Prominent projection on the occipital bone.

  • Occipital condyles: Articulate with the first cervical vertebra (atlas).

  • Foramen magnum: Large opening for the spinal cord.

• Temporal (2): Form the lower sides of the skull and part of the cranial floor.

  • Zygomatic process: Forms part of the cheekbone.

  • Mastoid process: Attachment for neck muscles.

  • External auditory meatus: Ear canal opening.

  • Styloid process: Attachment for tongue and neck muscles.

  • Mandibular fossa: Articulates with the mandible.

  • Sutures: Connects with other cranial bones.

• Sphenoid: Forms part of the base of the skull and sides of the orbits.

  • Sella turcica: Houses the pituitary gland.

  • Optic canal: Passage for optic nerve.

  • Superior orbital fissure: Passage for nerves and vessels.

  • Foramen ovale, rotundum, spinosum, lacerum: Openings for nerves and vessels.

• Ethmoid: Forms part of the nasal cavity and orbits.

  • Cribriform plate: Contains olfactory foramina.

  • Middle nasal concha: Increases surface area in nasal cavity.

C. Facial Bones (14)

• Maxilla (2): Upper jaw, forms part of the orbit and nasal cavity.

  • Alveolar margin: Contains tooth sockets.

  • Infraorbital foramen: Passage for nerves and vessels.

• Mandible: Lower jaw, only movable bone of the skull.

  • Body, ramus, mental foramen: Key features for muscle attachment and nerve passage.

• Zygomatic (2): Cheekbones.

• Nasal (2): Bridge of the nose.

• Lacrimal (2): Medial wall of orbit.

• Palatine (2): Posterior part of hard palate.

• Vomer: Forms part of nasal septum.

• Inferior nasal concha (2): Increases surface area in nasal cavity.

Foramina inside the Skull (in order)

• Optic canal

• Foramen rotundum

• Foramen ovale

• Foramen lacerum

• Foramen spinosum

• Internal acoustic meatus

• Jugular foramen

• Foramen magnum

B. Hyoid Bone

• Located in the neck, supports the tongue and is not directly attached to other bones.

Vertebral Column (24 vertebrae, 1 sacrum, 1 coccyx)

The vertebral column protects the spinal cord and supports the head and body. It is divided into regions based on vertebrae type.

• Cervical Vertebrae (7):

  • Atlas (C1): Supports the skull, no body.

  • Axis (C2): Has the dens, allows head rotation.

  • Transverse foramen: Only in cervical vertebrae, passage for vertebral artery.

• Thoracic Vertebrae (12): Articulate with ribs.

• Lumbar Vertebrae (5): Largest vertebrae, support most body weight.

• Sacrum:

  • Base and apex

  • Posterior sacral foramen

  • Median sacral crest

  • Sacral canal

  • Sacral promontory

• Coccyx: Tailbone, vestigial structure.

Thoracic Cage

The thoracic cage protects vital organs and supports the shoulder girdle and upper limbs.

D. Thoracic Cage

• Sternum:

  • Manubrium

  • Body

  • Xiphoid process

  • Jugular notch

  • Clavicular notch

• Ribs:

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

  • False ribs (8-10): Attach indirectly to sternum.

  • Floating ribs (11-12): No anterior attachment.

• Costal cartilage: Connects ribs to sternum.

Appendicular Skeleton

The appendicular skeleton includes the bones of the limbs and the girdles that attach them to the axial skeleton.

A. Pectoral Girdle and Upper Limb

• Clavicle: Collarbone, connects arm to trunk.

• Scapula: Shoulder blade.

  • Spine, acromion, coracoid process, glenoid cavity, supraspinous fossa, infraspinous fossa, subscapular fossa

• Humerus: Upper arm bone.

  • Head, greater tubercle, lesser tubercle, intertubercular groove, deltoid tuberosity, capitulum, trochlea, medial/lateral epicondyle, olecranon fossa, radial fossa

• Radius: Lateral bone of forearm.

  • Head, radial tuberosity, styloid process, ulnar notch

• Ulna: Medial bone of forearm.

  • Trochlear notch, olecranon process, coronoid process, styloid process, radial notch

• Carpals (8): Wrist bones.

  • Scaphoid, lunate, triquetrum, pisiform, trapezium, trapezoid, capitate, hamate

• Metacarpals (5): Palm bones, numbered I-V from thumb side.

• Phalanges (14): Finger bones, proximal, middle, and distal (thumb has only proximal and distal).

B. Pelvic Girdle and Lower Limb

• Os Coxae: Hip bone, formed by fusion of ilium, ischium, and pubis.

  • Acetabulum: Socket for femur.

  • Obturator foramen: Large opening for nerves and vessels.

  • Auricular surface, greater sciatic notch

• Ilium: Superior part of hip bone.

• Ischium: Inferior, posterior part of hip bone.

  • Ischial tuberosity, lesser sciatic notch, ischial spine, iliac crest

• Pubis: Anterior part of hip bone.

  • Pubic symphysis

• Femur: Thigh bone, largest bone in body.

  • Head, neck, greater/lesser trochanter, linea aspera, lateral/medial epicondyle, patellar surface, intercondylar fossa

• Patella: Kneecap.

  • Base, apex

• Tibia: Medial bone of lower leg.

  • Tibial tuberosity, medial/lateral condyle, intercondylar eminence, anterior border/crest, medial malleolus, fibular notch

• Fibula: Lateral bone of lower leg.

  • Head, lateral malleolus

• Tarsal Bones (7): Ankle bones.

  • Calcaneus, talus, navicular, cuboid, medial/intermediate/lateral cuneiform

• Metatarsal Bones (5): Foot bones, numbered I-V from big toe side.

• Phalanges (14): Toe bones, proximal, middle, and distal (big toe has only proximal and distal).

Key Bone Features Table

The following table summarizes key bone features and their functions or locations.

Additional info:

• Bone markings such as foramina, processes, and notches are important for the passage of nerves and blood vessels, and for muscle attachment.

• Understanding the location and function of each bone and feature is essential for identifying skeletal anatomy in clinical and laboratory settings.