Vertebrata, a name applied by Lamarck to the highest branch of the animal kingdom, from its being characterized by a bony or cartilaginous internal skeleton, of which the most essential and persistent portion is the vertebral column or spine. (See Comparative Anatomy, Philosophical Anatomy, and Skeleton.) Aristotle had made the distinction of ivaifia (blood animals) and avaifia (bloodless animals), corresponding respectively to the vertebrata and invertebrata of Lamarck. Oken called the vertebrates sarcozoa or flesh animals; Ehrenberg, myeloneura; De Blainville, osteozoaria; and Owen, myelencephala. These various terms describe very accurately the relations of the skeleton, red blood, muscles, and cerebro-spinal nervous centres, characteristic of fishes, batrachians, reptiles, birds, and mammals. The essential character of the spinal column is to have a distinct cavity above the axis for the nervous centres, and another below for the organs of vegetative life, both circumscribed by complicated bony arches.

Vertebrates are the doubly symmetrical type of Von Baer, their embryological development producing identical parts arising on both sides of an axis, growing upward and downward and shutting up along two lines, the inner layer of the germ being enclosed below and the upper above; Van Beneden calls them hypocotyledones or hypovitellians, from the vitellus or yolk entering the body from the under or ventral side. Lamarck also styles them intelligent animals, but comparative psychology is not sufficiently advanced to enable us to distinguish in this way between the sensations of a fish and a cephalopod or an insect. In vertebrates reproduction is sexual, without normal hermaphroditism, and the jaws move vertically and not laterally. Ehrenberg divides vertebrates into nutrientia, or warmblooded, and taking care of their young, like mammals and birds; and orphanozoa, coldblooded, taking no care of their young, like reptiles and fishes; but some of the latter do take care of their young, in a different or in the same way as the former division. The classes of vertebrates, according to Agassiz, are: 1, myzonts (myxinoids and cyclostomes); 2, fishes proper; 3, ganoids (sturgeons, etc.); 4, selachians (sharks and rays); 5, amphibians (frogs, salamanders, etc.); 6, reptiles; 7, birds; and 8, mammals.

In this type, to use his words ("Atlantic Monthly," January, 1862, p. 12), "the head is the prominent feature; it is, as it were, the loaded end of the longitudinal axis, so charged with vitality as to form an intelligent brain, and rising in man to such predominance as to command and control the whole organism." The classification adopted by Prof. Owen is as follows: I., pieces, with the subclasses dermopteri (cirrostomi, cyclostomi), teleostomi (malacopteri, anacanthini, acanthopteri, plectognathi, lophobranchii, ganoidei), plagiostomi (holocephali, plagiostomi), and protopteri (lepidosiren); II., amphibia, with the orders ophiomorpha, ichthyomorpha, theriomorpha, and labyrinthodontia; III., reptilia, with the orders chelonia, lacertilia, ophidia, crocodilia, and the extinct ichthyopterygia, sauropterygia, anomodontia, dinosauria, and pterosauria; IV., aves, divided into the three sections of altrices (embracing the raptores, scansores, volitores, and cantores), proecoces (rasores, cursores, grallatores, natatores), and uroioni (archseopteryx); V., mammalia, with the four subclasses of archencephala (bimana), gyrencephala (quadrumana, carnivora, artiodactyla, perissodactyla, proboscidia, toxodontia, sirenia, cetacea), lissencephala (bruta, cheiroptera, insectivora, rodentia), and lyencephala (marsupialia, monotremata). Huxley makes the vertebrata his sixth subkingdom, characterized by the body composed of definite segments arranged longitudiaally or one behind the other.

The main masses of the nervous system are on the dorsal aspect, and are completely shut off from the general body cavity. The limbs, when present, are turned away from that side of the body on which the main nervous masses are situated, and are never more than four. He divides the vertebrata into three primary provinces, viz.: ichthyopsida (fishes and amphibians), sauropsida (reptiles and birds), and mammalia. His classes are the following: I., pisces, with the orders pharyngobranchii, marsipobranchii, teleostei, ganoidei, elasmoIranchii, and dipnoi; II., amphibia, with the ordersurodela, labyrinthodontia, gymnophiona, and anoura; III., reptilia, with the orders chelonia, lacertilia, ophidia, crocodilia, plesiosauria, ichthyosauria, dicynodontia, ornithoscelida, and pterosauria; IV., aves, with the groups ratitoe (with the sternum devoid of a keel), carinatoe (sternum provided with a keel), and saururoe; V., mammalia, with the groups ornithodelphia (monotremata), didelphia (mar8upialia), and monodelphia (edentata, ungulata, toxodontia, sirenia, cetacea, hyracoidea, proboscidea, carnivora, rodentia, insectivora, cheiroptera, and primates). For further details of his classification of birds, see Ornithology. Modifications of these classes and orders are almost as numerous as the specialists who have investigated them, and chiefly of interest to students of the history of zoology.