The eye is small, and the external ear represented by a minute aperture, scarcely larger than would be made by a pin, about 2 in.
The sense-organs are highly developed; the wing-membranes are exceedingly sensitive; the nose-leaf is also an organ of perception, and the external ear is specially modified to receive soundwaves.
They may be characterized as very elongated reptiles without limbs (unless with tiny vestiges of posterior limbs), without eyelids and external ear openings, with the teeth anchylosed to the supporting bones, a bifid slender tongue which is telescoped into its basal half, and with a transverse vent.
The external ear consists of the auricle and the external acoustic meatus or ear canal.
An adjunct test of audiometry is acoustic immitance testing which assesses the facility with which sound can travel from the external ear to the cochlea inside the ear.
