PASSHRES, Hal 
of the essential features of this organ, in so far as they concern 
the systematist, nay be welcome. 
The syrinx is the term applied to the lower end of the wind- 
pipe and the adjacent ends of the bronchi in birds, wherein these 
portions have become variously modified to form the organ of 
voice, which, in Mammals, is formed by the larynx—the upper 
end of the windpipe. But while in the Mammals the larynx is a 
comparatively stable structure, in the birds the syrinx presents a 
very remarkable range of differences both in regard to its funda- 
mental structural characters, as well as of musculature. 
Tor the present it must suffice to give a brief survey of the 
essential features of the syrinx in the Passeres and, for systematic 
purposes, the musculature is the dominant factor. 
The syrinx, then, in this Group presents wide contrasts, 
even among Genera of the same Family, but nevertheless it 
conforms in its essential characters with that of the Aves as a 
whole. That is to say, it is formed of a number of bony or 
cartilaginous rings and semi-rings—some of which may be com- 
pletely or partially welded—held together by thin membranes 
which serve not merely to support the framework, but also in the 
production of the ‘ voice.” 
In the Anisomyodi the syringeal muscles are inserted either in 
the middle or on to the dorsal or ventral ends of the semi-rings. 
Syrinx of Pitta angolensis (after Garrod, P.Z.S. 1876, pl. hii), showing the 
Anisomyodian attachment of the intrinsic muscles at the middle of the bronchial 
semi-rings. There is also a single pair of bronchial muscles, continued down 
from the sides of the windpipe, insignificant in size, quite lateral, and termi- 
nating by being inserted into the middle of the outer surface of the second 
bronchial semi-ring, 
In the Diacromyodi these muscles are inserted into both ends 
of the semi-rings. They may be limited always to one pair as 
in Clamatores, to two as in Oligomyodi and some Tracheophone 
or there may be as many as seven pairs as in the Oscimes. 
But the structure of the syrinx itself, as apart from its 
musculature, has been, and still is, a feature of importance in 
