There remains but one logical way, namely, to distinguish as follows: - (i) Passeres anisomyodi, in which the syrinx muscles are unequally inserted, either on the middle or on one end of the semi-rings, either dorsal or ventral.
But indications of such a syrinx occur also in Pittidae, pigeons and gallinaceous birds (Gallidae), the last cases being clearly analogous.
The syrinx or lower larynx is the most interesting and absolutely avine modification, although absent as a voice-producing organ (probably due to retrogression) in most Ratitae, storks, turkey buzzards (Cathartes) and Steganopodes.
According to the position of the chief sound-producing membranes, three types of syrinx are distinguishable: - (i) Tracheo-bronchial, by far the commonest form, of which the two others are to a certain extent modifications.
Whilst the type of syrinx affords no help in classification, it is very different with its muscles.
A lover of music, he invented the shepherd's pipe, said to have been made from the reed into which the nymph Syrinx was transformed when fleeing from his embraces (Ovid, Metam.
The syrinx consisted of a varying number of reeds, having their open ends or embouchures in a horizontal line and their stopped ends, formed by the knots in the reed, gradually decreasing in length from left to right.
This way of using the characters of the syrinx for the classification of the Passeriformes seems simple, but it took a long time to accomplish.
The syrinx is a modification of the lower part of the trachea and of the adjoining bronchi.