Scarcely any two modern ornithologists are agreed as to the affinities Between the Rollers and several other groups of Picarian birds, especially the Kingfishers, Bee-eaters, Hornbills, Hoopoes, Swifts, and Nightjars*. All these, except the Hoopoes, have a peculiar and variable arrangement of the deep plantar tendons (see Garrod, P. Z. S. 1875, p. 344). The two tendons coalesce more or less completely either before their subdivision to supply the different digits or below the point at which a slip leaves the flexor perforans digitorum to supply the hallux.
In other respects, such as the characters of the palate and sternum, the form of the dorsal feather-tracts, presence or absence of caeca, and the nature of the oil-gland, whether nude or tufted, there is much variation, and the majority of the families mentioned differ from each other quite as much as the Passeres and Eurylaemi do. It appears very doubtful whether the Swifts have any affinity to the other groups, and the Caprimulgidae and Podargidae are also isolated. In adopting Gadow's arrangement and leaving the Coraciadae or Rollers, Meropidae or Bee-eaters, Alcedinidae or Kingfishers, Bucerotidae or Hornbills, and Upupidae or Hoopoes in one order, I am very largely influenced by a desire to avoid increasing the number of ordinal groups.
The Anisodactyli have a desmognathous palate; basipterygoid processes are rudimentary or absent. Sternal characters vary. There is no ambiens muscle. A hallux is always present, and there are almost constantly three anterior toes, more or less joined together at the base. All the species lay white eggs in a hole, either in a tree or in the ground, and the young are hatched naked. The sexes are alike as a rule, but when they differ in plumage the young resemble adults of the same sex.
There are five Indian suborders, thus distinguished :—
a. Oil-gland nude ; caeca present; 4 notches behind sternum.
a1. Two carotids; manubrium sterni simple, no foramen behind it………………………….CORACIAE.
b1. Left carotid only; manubrium sterni complex and having behind it a perforation to receive ends of coracoids ………………………….MEROPES.
b. Oil-gland tufted ; caeca absent.
c1. Pour notches behind sternum………………………….HALCYONES.
d1. Two notches behind sternum.
a2. No lateral bare tracts (apteria) on neck ; 11 primaries………………………….BUCEROTES.
b2. Lateral cervical apteria present; 10 primaries………………………….UPUPAE.
The South-American Motmots and W. Indian Todies also belong here.
* Compare Garrod, P. Z. S. 1874, p. 117; Sclater, Ibis, 1880, p. 401; Forbes, Ibis, 1881, p. 31 ; Seebohm, Classification of Birds and Supplement; Furbringer, Untersuchungen, p. 1567; Sharpe, Review of Recent Attempts to Classify Birds, pp. 79-81; Gadow, P. Z. S. 1892, p. 251. See also vols, xvi and xvii of the British Museum Catalogue of Birds.
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