regarded by all ornithologists as a distinct order, and the highest of the class. But in the present volume a general scheme of classification became a necessity : the arrangement hitherto adopted in the majority of works on Indian Ornithology Legge's ' Birds of Ceylon ' and Oates's ' Birds of Burmah' being the most important exceptions has been that of Jerdon's great work, and was taken from G. B. Gray's, which again was but slightly modified from that of Cuvier. This classification, proposed in the early part of the present century, when the anatomy of birds had received but little attention, was founded exclusively on the characters of the beak and feet. It was soon found that there were defects in the Cuvierian system, one of the leaders in the path of reform being Edward Bly th, the pioneer of Indian scientific ornithology; but it was long before a satisfactory natural system could be devised, and even now birds are by no means so clearly arranged, or divided into orders so well defined, as mammals and reptiles are. Still some of the later attempts to arrange the intricate groups of birds have been fairly successful in consequence of their depending not on one or two characters but on several, of their taking into consideration both internal anatomy and external structure, and of their making use of such clues to affinity as are afforded by nidification, oology, and the changes of plumage in the young.
The system adopted in the present work is, in the main, identical with those of Sharpe and Gadow, and differs in no important point from the classifications of Sclater and Newton. References will be found on page 15. The chief difference between the plan here followed and those proposed by the ornithologists named, is that no attempt has been made in the present work to arrange in larger categories the groups here termed orders. This is due to the circumstance that there is a much wider general agreement as to the distinctness of the smaller ordinal or subordinal groups than as to their relations to each other.
The principal anatomical characters by which the different orders are distinguished are furnished by the bones of the palate, shoulder-girdle and sternum, and the vertebrae ; by the occurrence of cseca in the intestines, the presence or absence of particular muscles in the thigh, and the characters of the deep plantar tendons. Amongst the external characters, pterylosis, or the disposition of the feathers with regard to the clad and naked tracts of the body (pterylæ and
