[720] The acetabulum, or socket for the head of the thigh-bone, is always perforated. The femur has a surface for the articulation of the fibula; and by this character the femur of all birds may be distinguished. There is always a patella.
[721] The lower end of the tibia is very like that of the femur.
The toes of birds present deviations equally recognisable; for the number of the articulations (or phalangeal pieces of bone) in each toe is different. Thus the thumb, or short toe, has two bones; the first toe on the inner side three; the the middle toe four; and the outer toe five. In general, three toes are directed forwards, and one backwards. In some species, the thumb or opposable toe is altogether wanting; in others, as in the swallow, it is directed forwards; in climbing birds, both the outer and the back toe are situated behind. The position of the hind toe, therefore, affords an important indication of the habits of the bird (see Wond. p. 146, Lign. 23), and from a fragment of the lower extremity of the shank or tarso-metatarsal bone, with any trace of this articulation, we may determine whether the individual to which it belonged was a climber, wader, &c. In the toes of Crocodiles alone, the number of joints is the same as in birds; but in these reptiles, each toe is supported by a distinct metatarsal bone. The osteological peculiarities above enumerated may assist the collector in arriving at some general inferences as to the nature of any fossil remains of birds.
FOSSIL BIRDS.
II. Ornitholites, or Fossil Birds.—The fossil remains of birds consist in general of their osseous skeletons, and of detached bones, and rarely of the feathers and eggs.
Pleistocene Epoch.—Bones of the Dodo[722] (see Wond. p. 131), a bird which appears to have become extinct by human agency within the last two centuries, have been found, associated with the remains of a recent species of Tortoise, beneath a bed of lava in the Isle of France. And in some caverns in the island of Rodriguez, the bones of one or more large birds allied to the Dodo have also been discovered.
[722] See Penny Cyclopædia, Art. Dodo, and the beautiful work on the natural history of the Dodo and its Kindred, by the late lamented Mr. Strickland and Dr. Melville, 4to.
Dinornis (fearfully great bird). Pict. Atlas, frontispiece, and p. 172—Numerous bones of large extinct birds have been obtained in New Zealand by Mr. Rule, the Rev. W. Williams, Col. Wakefield, Mr. Walter Mantell, and others. These have been referred by Professor Owen to tridactylous struthious birds (one of which was one-third larger than the African ostrich), resembling the living Apteryx of New Zealand (Wond. p. 128, Petrif. p. 106) in the proportions of the tibia to the metatarsus, and also in the rudimental state of the wings. The bones are found in the recent alluvium, but probably in some cases at least they have been washed by the streams from older alluvial deposits.
An account of the history of the discovery of the gigantic Moa’s bones in New Zealand (Wond. p. 129) is given in full in Petrif. p. 93, et seq.; and the scientific description of the various parts of the skeleton of the Dinornis and Palapteryx, chiefly collected from Professor Owen’s elaborate and finely illustrated memoirs in the Transactions of the Zoological Society, should be consulted, Petrif. p. 108, &c. Of Dinornis Professor Owen discriminates seven or eight species; of Palapteryx, three species; and indications of a species of a third associated genus, Aptornis.
Fragments of egg-shell accompany these interesting relics of birds from New Zealand. From Madagascar also bird-bones and eggs have been obtained in a fossil state, that indicate the original bird (Æpyornis) to have been even of a greater size than the Dinornis.