Anatomy of the Skull

Bones of the Skull

• The human skull consists of two main types of bones: cranial and facial bones
• There are 8 cranial bones:
  • Frontal (1)
  • Parietal (2)
  • Occipital (1)
  • Temporal (2)
  • Sphenoid (1)
  • Ethmoid (1)
• There are 14 facial bones:
  • Mandible (1)
  • Maxillae (2)
  • Lacrimal (2)
  • Nasal (2)
  • Palatine (2)
  • Zygomatic (2)
  • Inferior nasal conchae (2)
  • Vomer (1)
• Cranial bones are larger and contribute to protecting the brain
• Facial bones contribute to features like the nose, cheekbones and jawline
• Some skull bones are paired and some are unpaired

Cavities of the Skull

• The skull contains several cavities that house softer structures
• These cavities include:
  • Cranial cavity
    • Houses the brain
  • Orbits
    • House the eyeballs and muscles that move them
  • Nasal cavity
    • Responsible for breathing and smell
  • Oral cavity
    • Responsible for chewing food and speech
  • Paranasal sinuses
    • Air-filled cavities that help to lighten the skull and modify the voice

Frontal Bone

• Forms the forehead and part of the cranium
• Features:
  • Glabella
    • Smooth area between the eyebrows
  • Supraorbital margin
    • Bony rim above the eye socket
  • Supraorbital foramen
    • Opening above the eye socket that allows passage of a blood vessel and nerve

Mandible

• Forms the lower jaw
• The only moveable bone of the skull
• Features:
  • Body, ramus, and angle
    • Body is the horizontal portion, ramus is the vertical portion, and angle is the point where the two meet
  • Coronoid and condylar processes
    • Serve as points of attachment for muscles
  • Mandibular notch
    • Indentation between the processes
  • Mental foramina
    • Openings on the anterior surface that allow passage of blood vessels and nerves
  • Mental protuberance
    • Point on the chin

Maxillary Bone

• Also called the hard palate or maxilla
• Forms the upper jaw, most of the roof of the mouth, part of the orbit, and the lateral base of the nose
• Features:
  • Alveolar processes
    • Contain the sockets for the teeth
  • Infraorbital foramen
    • Opening below the eye socket that allows passage of a blood vessel and nerve

Lacrimal Bones

• Form part of the orbit
• Contain lacrimal glands that secrete tears

Palatine Bones

• Form the posterior portion of the hard palate, the medial part of the orbit, and contributes to the vertical section of the nasal cavity

Zygomatic Bones

• Known as the cheekbones
• Form much of the lateral part of the orbit
• Features:
  • Temporal process
    • Unites with the zygomatic process of the temporal bone to form the zygomatic arch

Vomer, Nasal, and Inferior Nasal Conchae Bones

• Vomer
  • Forms part of the nasal septum
• Nasal bones
  • Form the bony base (bridge) and lateral walls of the nose
• Inferior nasal conchae
  • Project into the nasal cavity

Sutures

• Immobile joints filled with dense, fibrous connective tissue that attach cranial bones
• Main sutures:
  • Sagittal suture
    • Connects the two parietal bones
  • Coronal suture
    • Connects the frontal bone to the parietal bones
  • Lambdoid suture
    • Connects the parietal bones to the occipital bone
  • Squamous suture
    • Connects the parietal and temporal bones

The Orbit

• Protects the eyeball and muscles that move it
• Bones contributing to the orbit:
  • Frontal, zygomatic, maxilla, ethmoid, lacrimal, palatine, and sphenoid
• Features:
  • Optic canal
    • Allows entry of the optic nerve
  • Superior orbital fissure
    • Allows entry of blood supply

The Appendicular Skeleton

• Consists of:
  • Bones found in the upper and lower limbs
    • Upper limbs: humerus, ulna, radius, carpal bones, bones of the hand
    • Lower limbs: femur, tibia, fibula, patella, tarsal bones, bones of the foot
  • Bones that attach the limbs to the axial skeleton
    • Shoulder girdle: clavicle and scapula
    • Pelvic girdle: os coxae

Bones of the Shoulder Girdle

• The clavicle and scapula compose the shoulder girdle
• Anchor the upper limb to the axial skeleton
• Facilitate movement of the upper limb
• Serve as attachment sites for muscles that move the shoulder and arm

Clavicle

• Also known as the collarbone
• Loosely-anchored, S-shaped bone
• Articulates medially with the manubrium of the sternum
  • Forms the sternoclavicular joint
• Articulates laterally with the acromion of the scapula
  • Forms the acromioclavicular joint

Scapula

• Located on the posterior of the shoulder
• Features:
  • Glenoid cavity
    • Articulates with the head of the humerus to form the glenohumeral joint
  • Coracoid and acromion processes
    • Serve as points of attachment for muscles
  • Scapular spine
    • Ridge on the posterior surface
  • Supraspinous, infraspinous, and subscapular fossae
    • Depressions on the anterior and posterior surfaces that house muscles
• Borders:
  • Superior, medial, and lateral borders
• Angles:
  • Superior and inferior angles

Femur

• Found in the thigh region
• Longest, strongest bone of the body
• Head articulates with the acetabulum of the os coxae to form the hip joint
• Multiple markings for muscle attachment
• Medial and lateral condyles articulate with the tibia to form the knee joint

Patella

• Largest sesamoid bone of the human body
• Only sesamoid bone found in all humans
• Increases leverage power of thigh muscles

Tibia and Fibula

• Found in the lower leg
• Tibia
  • Medial bone
  • Condyles articulate with the femur to form the knee joint
  • Tibial tuberosity
    • Bump on the anterior surface where the patellar ligament attaches
  • Medial malleolus
    • Bony projection at the medial side of the ankle that articulates with the talus
• Fibula
  • Lateral bone
  • Head
    • Proximal end that articulates with the tibia
  • Lateral malleolus
    • Bony projection at the lateral side of the ankle that articulates with the talus

Bones of the Foot: Tarsals

• Proximal row of tarsals:
  • Talus
    • Articulates with the tibia and fibula to form the ankle joint
  • Calcaneus
    • Largest tarsal bone; forms the heel
  • Navicular
    • Articulates with the talus and three cuneiform bones
• Distal row of tarsals:
  • Cuboid
    • Articulates with the calcaneus, navicular, and fourth and fifth metatarsals
  • Medial, intermediate, and lateral cuneiform
    • Articulate with the navicular and metatarsals

Bones of the Foot: Metatarsals and Phalanges

• Metatarsals
  • Make up the arch of the foot
  • Numbered 1–5 (I–V) starting at the medial side of the foot
• Phalanges
  • 14 phalanges in the toes
  • Toes numbered 1–5 starting at the big toe (hallux)
  • Named proximal, middle, and distal according to relative position
  • Hallux only has proximal and distal phalanges