_Fregata_ differs from all other ornithic forms in the fact that the furcula also coalesces with the coracoids at its extremities, while the coracoids again unite firmly with the scapula, producing an almost rigid framework, considered by Professor Newton to be connected with the power which the bird possesses of sustaining itself nearly motionless in the air.[74] The peculiar angular articulation of the long eighth cervical vertebra in _Plotus_, which causes the Z-shaped "kink" in the neck, must also be noticed here.[75] The tongue is rudimentary; the nostrils are pervious in _Phaëthon_, impervious elsewhere, being practically obliterated in adults; the syrinx is tracheo-bronchial, except in _Sula_ and _Pelecanus_, where the usual muscles are entirely absent. The subcutaneous air-cells of _Sula_ are most remarkable. The newly-hatched young are blind and helpless, being naked and covered with blackish skin in _Sula_, _Phalacrocorax_, _Plotus_, and _Pelecanus_, though they soon acquire a white downy coat; in _Phaëthon_ and _Fregata_ they are similarly clothed on breaking the shell. The down of the adults is uniformly distributed, the aftershaft is diminutive or wanting. The gular sacs, horny excrescences on the beak, crests, and so forth, are noted below. Fam. I. PHAETHONTIDAE.–_Phaëthon aethereus_, _P. flavirostris_, and _P. rubricauda_ are chiefly found in the tropical regions of the south; but the first two species breed about as far north as the tropic of Cancer, while they frequent the West Indies, and occasionally stray to the Eastern United States, or even Newfoundland.[76] The third inhabits the southern seas and the Indian Ocean. All these Tropic- or Boatswain-birds, as they are denominated, have satin-like white plumage–often with a tinge of pink–varied by blackish bars or patches above, and black marks near the eye; the bill is red, or in _P. flavirostris_ yellow, the metatarsi yellowish and the toes chiefly black. In _P. rubricauda_ the long stiff median rectrices are dull red with black shafts and very narrow webs, in _P. flavirostris_ they are pinkish with similar shafts, and in _P. aethereus_ entirely white. The sexes are alike, the young being more irregularly marked and having no long tail-feathers.