The structure of the bill of the Parrots is so remarkable as to be worthy of a more extended description than could be given to it when it was incidentally referred to in our account of the osteology of birds in general. The way, however, in which the upper and lower jaws are connected with the skull was there explained, and a reference to the description on pp. 241–2 will save the necessity of much repetition now. That account embraced all members of the class of birds; here we are dealing only with certain peculiar modifications.
If the skull of an adult bird of any familiar type, such as a Crow, be examined, it will be seen that the bones of the upper jaw are apparently continuous, and form one piece, with those of the forehead and sides of the head. There is nothing that looks like a joint, or “articulation,” between the bill where it is attached to the forehead above, or to the long jugal arch (“quadrato-jugal”) that runs each side to reach the quadrate bone, or to the flattened bones that help to form the palate below. But if the skull of this same bird had been carefully examined in an earlier stage of its existence, it would have been found that the bones were at first distinctly separate at the three points here indicated, and were merely connected by a soft membranous substance. In many birds this “inter-osseous” membrane connecting the bones of the upper mandible with the skull proper never becomes true bone at all, but remains throughout life more or less soft and flexible. And by this means a sort of elastic joint is established, conferring upon the beak a certain range of up and down motion.
Now in Parrots, more conspicuously than in any other birds, each of these joints, not alone that of the beak with the forehead, is converted into a true hinge-like articulation, so that the upper jaw can be raised to a very considerable extent; and to effect this motion the muscles of the palate are developed into a somewhat complex apparatus.
If the figure be examined, the actual relations of the bones can be readily made out. At a is seen the line where the bill is articulated to the frontal bones. At b is the joint which the bill makes with the long jugal bone (j). And at c is its articulation with the palatine bone (pl).
SKULL OF THE GREY PARROT.
But it is not this mobility of the upper mandible alone that gives the characteristic aspect to the Parrot’s face. There are several other points in which Parrots agree, with a wonderful uniformity, among themselves, and differ from most other birds. Besides the absence of certain important processes, called “basi-pterygoid,” the ploughshare-like bone, or “vomer,” is altogether wanting. The maxillo-palatines are very largely developed and spongy; they unite with one another in the middle line, and with the thick wall of bone into which the septum nasi is in Parrots strongly ossified, and thus fill up almost the whole base of the beak. The long palatine bones proper are remarkably flattened from side to side for most of their length; their hinder edges are more or less notched, and quite free from any bony attachment; and they are united at about the hinder third of their length by a plate-like extension from each. The scoop-like lower mandible, with its tip that seems to have been cut off “square,” to be out of the way of the strongly-hooked upper jaw, is too familiar to call for any particular description.
THE SECOND ORDER.—PICARIAN BIRDS SUB-ORDER I.—ZYGODACTYLÆ.
CHAPTER VIII.
CUCKOOS—HONEY GUIDES—PLAINTAIN-EATERS—WOODPECKERS—TOUCANS—BARBETS.
[THE CUCKOOS]—THE BUSH CUCKOOS—THE LARK-HEELED CUCKOOS, OR COUCALS—THE COMMON CUCKOO—Its Characteristics—Mrs. Blackburn’s Account of a Young Cuckoo Ejecting a Tenant—Breeding Habits—The Eggs—The Call-notes of Male and Female—Food—Its Winter Home—Its Appearance and Plumage—[THE HONEY GUIDES]—Kirk’s Account of their Habits—Mrs. Barber’s Refutation of a Calumny against the Bird—[THE PLANTAIN-EATERS]—[THE WHITE-CRESTED PLANTAIN-EATER]—[THE GREY PLANTAIN-EATER]—[THE COLIES]—[THE WHITE-BACKED COLY]—[THE WOODPECKERS]—How they Climb and Descend Trees—Their Bill—Do they Damage Sound Trees?—[THE WRYNECKS]—[THE YAFFLE]—[THE RED-HEADED WOODPECKER]—[THE SPOTTED WOODPECKER]—[THE TOUCANS]—Mr. Gould’s Account of their Habits—Mr. Waterton’s Account—The Enormous Bill—Azara’s Description of the Bird—Mr. Bates’ History of a Tame Toucan—[THE BARBETS]—Messrs. Marshall’s Account of the Family—Mr. Layard on their Habits.