These vascular membranes are called the lateral septa.
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.
Elastin occurs either as thick strands or as membranes; it constitutes the " elastic tissue " of the anatomist.
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.
External tympaniform membranes exist, with great variations, between the specialized one or two last tracheal and some of the first bronchial rings.