This order includes the vast majority of living birds. The cervical vertebrae have saddle-shaped articulating surfaces (except in the Ichthyornithiformes). The posterior caudal vertebrae are ankylosed forming a pygostyle. The quadrate articulates with the cranium by a double head. In all except the Tinamidae the vomers are narrow behind and not interposed between the palatines, pterygoids and basisphenoidal rostrum. The sternum has a median keel, and the anterior limbs are in the great majority of cases adapted for flight. Clavicles are well developed, and the scapula and coracoid are nearly at right angles to one another. The various groups into which the Carinatae are divisible are shown in the table on pp. 40-42. Their special characters will not be dealt with. [Illustration FIG. 55. _Gallus bankiva_ var. _domesticus_. THE LEFT HALF OF THE SKELETON. The skull, vertebral column, and sternum are bisected in the median plane. (After Marshall and Hurst.) A, acetabulum. B, cerebral fossa. CB, cerebellar fossa. CL, clavicle. CO, coracoid. CR, cervical rib. C 1 = one, first cervical vertebra. FE, femur. HC, ventral end of clavicle. HU, humerus. HY, hyoid. IF, ilio-sciatic foramen. IL, ilium. IS, ischium. L, lachrymal. MC 3, postaxial metacarpal. MN, mandible. MS, xiphoid processes. MT, tarso-metatarsus. MT 1, first metatarsal. N, nasal. OP, optic foramen. P, premaxillae. PB, pubis. PL, palatine. PY, pygostyle. R, radius. RC, radial carpal. S, keel of sternum. SC, scapula. T, tibio-tarsus. TH 4, fourth thoracic vertebra. U, ulna. UC, ulnar carpal. UP, uncinate process. Z, infra-orbital bar. 1, 2, 3, 4, first, second, third and fourth digits of pes. 3, pre-axial, 4, middle, and 5, postaxial digit of manus.] FOOTNOTES: [94] M. Fürbringer, _Untersuchungen zur Morphologie und Systematik der Vögel_, I. and II. Amsterdam, 1888. Cf. H. Gadow, _Nature_, XXXIX. 1888, pp. 150 and 177. T.H. Huxley, "On the classification of birds." _P.Z.S._, London, 1867. E. Selenka and H. Gadow, _Vögel_ in Bronn's _Classen und Ordnungen des Thierreichs_ 1869-1890. [95] See p. 283. [96] R. Owen, _Phil. Trans._, vol. CLIII., p. 33; 1863. T.H. Huxley, _P. R.S._, vol. XVI., p. 243; 1868. C. Vogt, _Rev. Scient._, ser. 2, tom. 9, p. 241; 1879. C.H. Hurst, _Nat. Sci._, vol. III., p. 275; 1893; vol. VI., pp. 112, 180, 244; 1895. W.P. Pycraft, _Nat. Sci._, vol. V., pp. 350 and 437; 1894; and vol. VIII., p. 261; 1896. [97] According to Hurst the fourth and fifth digits are also present. [98] See C.W. Andrews, _P.Z.S._, 1894, p. 108. [99] See T.J. Parker, _Tr. Zool. Soc. London_, vol. XIII., pt. 2, 1895, and F.W. Hutton, several papers in _Tr. N. Zealand Inst._, 1893 and 1895. [100] See O.C. Marsh. _Odontornithes. A monograph of the extinct toothed birds of N. America._ New Haven, 1880. CHAPTER XVIII. THE SKELETON OF THE WILD DUCK (_Anas boschas_). I. EXOSKELETON.