1. Axial skeleton 

• Skull 
  • Skulls are made up of flat bones joined by sutures (immovable joints).
  • Skull is the framework of the face and support the teeth.
  • The lower jaw (mandible) is movable and allow mouth opening and closing.
  • The cranium protects the brain.

• Ribcage (Sternum & ribs)
  • 12 pairs of ribs articulate with the sternum and thoracic vertebrae.
  • Ribs and sternum form a cage to protect the heart and lungs.
  • The sternum is a flattened, narrow bone and ribs are curved bones.

• Vertebral column
  • Consist of 33 vertebrae attached to form a strong & flexible column. There are 5 types of vertebrae.
  • It protects the spinal cord, support the head, provides a base for back muscle attachment and provides an articulating surface for ribs and pelvic girdle.

• Has large neural canal
• No centrum
• Has two transverse foramina - allow arterioles to pass through brain
• Support the skull

• Odontoid process extends into ventral part of the neural canal of atlas and acts as pivot to allow the head to move side-to-side
• Has two transverse foramina
• Side-to-side head movement

• Broad and short transverse process
• Broad centrum
• Has two transverse foramina
• Support head and neck
• Attachment for neck muscles
• Has a short spinous process

• Has long spinous process which points backwards
• Support rib bones to form the rib cage and provide surface for attachment of muscles to the transverse process and centrum
• Muscle attachment to support head and neck
• Large and thick centrum
• Long transverse process

• The largest and strongest vertebra in the vertebral column
• Large and thick centrum
• Transverse process is long and flat
• Spinous process is short
• The large centrum supports the weight of the lower back

• Five bones fused together forming a broad
• Coccyx is formed by fusion of four vetebrae bones
• Balances and supports sitting position

• Bone attached together by fibrous connective tissue 
• No movement is allowed 
• These joints are categorised as sutures

• Bone attached together by cartilage 
• Movements are limited

• Bones joint together with synovial fluid 
• Movement in one plane or all planes
• These joints are known as synovial joints

• Characteristics: 
  • Not elastic 
  • Strong 
  • Connective tissue
• Function 
  • Joins muscle to bones
  • Transmits pulling force exerted by contraction of muscles to the bone and pull it up

• Characteristics 
  • Elastic 
  • Strong 
  • Connective tissue 
  • Flexible 
• Functions:
  • Join bone to bone 
  • Hold joints together 
  • Prevent dislocation 
  • Allow limited movement 

• Characteristic
  • A pair of muscles that work together 
  • When contracts, the other relaxes 
  • Examples: Biceps and triceps of the arm
• Functions: 
  • Exert pulling force onto bone 
  • Support movement and locomotion

• Has antagonistic muscles: circular muscle, longitudinal muscle.
• Hydrostatic skeleton: contraction and relaxation of antagonistic muscles raise hydrostatic pressure of the fluid in the coelom
• Chaetae: fine hooks which anchor to the ground

1. Posterior chaetae anchor the ground. Circular muscles in the anterior contract and the longitudinal muscles relax, producing high hydrostatic pressure. These cause the anterior segment to extend forward
2. Anterior chaetae anchor the ground. Posterior chaetae are withdrawn. Circular muscles in the anterior relax and longitudinal muscles contract, producing low hydrostatic pressure. These cause the posterior segments to be pulled forward
3. Continuos process - Peristaltic waves enable earthworms to move forward

• Scaly and slimly body to reduce water resistance
• W-shaped antagonistic muscle blocks are arranged in segments on both sides of a vertebral column named myotomes
• Swim bladder: an air sac inside the abdomen to maintain buoyancy
• Dorsal and ventral fins - prevent yawning and rolling
• Tail fin - forward thrust
• Paired fin (pelvic and pectoral fins) - steering, prevent pitching

1. Right myotomes contract, left myotomes to relax
2. Head and tail will bend to the right
3. Right myotomes relax, left myotomes contract
4. Head and tail will bend to the left
5. Continuous contraction and relaxation of muscles allow fish to move their tail
6. The tail movement creates a forward thrust

Antagonistic muscles:

1. Flexor muscles
2. Extensor muscles:

• Found inside the internal structure of the exoskeleton
• The hind legs are bigger and longer for jumping
• Movement is produced by contraction and relaxation of these muscles

Jumping:

1. At rest, flexor muscles contract, hind legs folded in the shape of "Z"
2. Extensor muscles contract and hind legs straighten 
3. Grasshopper jumps forward and upwards