VAN 221: Veterinary Splanchnology and Applied Anatomy (1+1)

BIOMECHANICS OF STRING

• The two ends of bow are linked by the sternum, linea alba and abdominal muscles particularly rectus abdominis. This string stretches the bow
• It has dorsal string made up of epaxial (dorsal to vertebrae) muscles (eg. Longissimus dorsi) which straightens the bow and ventral string made up of
  • Hypaxial (ventral to vertebrae) muscles (eg. Longus colli in cranial thoracic and cervical regions, psoar major and minor in caudal thoracic, lumbar and sacral regions,) form interrupted ventral string – this flexes bow and stabilizes bow with epaxial muscles
  • Abdominal muscles form – uninterrupted ventral string (oblique, transverse and rectus muscles particularly recti muscles)
  • This initerrupted ventral string is indirectly attached bow by interposition of thoracic skeleton cranially and pelvic bones caudally
  • The ventral uninterrupted string flex the bow in thoracolumbar region eg.back of sitting cat, leaping and galloping
• The string bears weight of the organs supported by the ribs, transverse and oblique abdominal muscles and their aponeurosis
• The part of the weight of the viscera rests directly on ventral abdominal wall (ventral string) and tends to arch the bow but elasticity of the bow and active contractions of the extensor muscles of the back oppose arching of bow by string
• The other part of organ weight is transferred to axis of body (bow) through ribs and abdominal muscles which stretches the bow that is resisted by string
• The string is flexed not only to the two ends of the bridge but is attached all along the bow
• The bow and string can alter the form by muscular action and participate in the movements of the body as a whole
• The possibility of overextension in the lumbar region where rib protection is not there is prevented by ventral longitudinal ligament and articular processes which are well developed
• When bow is arched dorsally by contraction of the abdominal muscles and sublumbar muscles – tendons and muscles of the top boom are stretched and the spinous processes separate while pressure on bottom boom is increased and the vertebral bodies are squeezed together excessively
• Excessive arching in this direction is countered by the discs, supraspinous ligament and longissimus dorsi muscles
• A type of cantilever is placed both infront and behind the bow of the bridge
• The function of the cantilever in animal body is to counter and thus balance the centrifugal thrust which develops in the bottom boom when the animal is moving. They also help in maintaining equilibrium
• The front cantilever is represented by the head and neck and caudal cantilever is represented by sacrum and tail
• By raising and lowering the front cantilever the centre of gravity of the body can be altered thereby shifting the overall balance
• In animals with long neck and heavy heads like horses and cattle the weight is carried mainly passively by the elastic ligamentum nuchae