The majority of birds possess a pair of internal tympaniform membranes forming the inner or median walls of the bronchi, which are there furnished with semi-rings only.
These vascular membranes are called the lateral septa.
This section comprehends three species only, known as Phalaropes or swimming sandpipers, which are distinguished by the membranes that fringe their toes, in two of the species forming marginal lobes,' and by the character of their lower plumage, which is as close as that of a duck.
When the connecting string is held taut and sounds, such as those of ordinary speech, are produced in front of one of the membranes, pulses corresponding to the fluctuations of the atmospheric pressure are transmitted along the string and communicated to the other membrane, which in its turn communicates them to the air, thus reproducing the sound.
Ical tele- Two disks of thin metal, or two stretched membranes, each furnished with a mouthpiece, are connected together by a thin string or wire attached at each end to the centres of the membranes.