Order XI. TUBINARES.
The Petrels seem to form a natural link between the Gulls and the Steganopodes. having a very strong external resemblance to the former, yet a closer structural affinity to the latter. They may be at once distinguished from all other birds by the impervious nostrils, which terminate externally in tubes, separate or united; the rhamphotheca, or "horny covering of the bill, is divided into several sections by deep grooves, as in some Steganopodes, whilst the upper mandible is generally much hooked at the end; the anterior toes are webbed throughout; the hallux is either small rudimentary or wanting, being frequently represented by the claw-phalanx alone; the wings are long; there are eleven primaries and the fifth secondary is absent; the oil-gland is present and tufted; the spinal feather-tract is w ell developed on the neck with lateral apteria and is forked on the back.
Petrels are schizognathous and holorhinal; the vomer is large., broad, depressed and pointed; cervical vertebrae fifteen; there are large supraorbital glands; there are two carotids ; the caeca are rudimentary or wanting; the femoro-caudal and semi-tendinosus muscles are always present, the ambiens and accessory femoro-caudal generally present, only absent in a few species.
The classification of the Petrels has been a much-debated question and was commented on by Blanford in the first edition of this work. Here it is perhaps unnecessary to comment at any length, beyond saying that further investigation will probably support those systematists who separate the Puffins (Puffinidae) which possess basipterygoid processes, from the Procellariidae, which have none.
So far as convenience goes and on account of the small number of genera and species occurring in India, it seems best to follow Blanford and retain them all in the one family Procellariidae. The Albatrosses do not come within the purview of this work and it is therefore needless to discuss their position.