Mechanism of hearing : The sound waves from sounding bodies strike the pinna. The pinna directs the waves into external auditory canal. These sound waves strike tympanum which starts vibrating.

Fig. V. S. Ear of man

(ii) Balance : The equilibrium is maintained by semicircular canals. The equilibrium is of two types :

1. Dynamic equilibrium : It is maintained by cristae present in amplullae of semicircular canals. When the head is rotating, at that time sensory hair get disturbed by moving endolymph. The disturbances are conducted to sensory cells and then to nerve fibres which transmit impulses to brain. It brings the organism in equilibrium.

2. Static equilibrium : When a man is running fast then otolith of maculae lag behind. These otolith come in contact with sensory hair and set up the message which is conducted to the brain and it brings the body in equilibrium.