Page:The Fauna of British India, including Ceylon and Burma (Birds Vol 1).djvu/43

of the essential features of this organ, in so far as they concern the systematist, may 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 fundamental structural characters, as well as of musculature.

For 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 completely 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. liii). 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 terminating 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 Tracheophonæ or there may be as many as seven pairs as in the Oscines. But the structure of the syrinx itself, as apart from its musculature, has been, and still is, a feature of importance in