VERTEBRATA, in zoology, a division of the animal kingdom, instituted by La marck, comprising animals in which the body is composed of a number of defi nite segments, arranged along a longitu dinal axis; the nervous system is in 14 main masses dorsal, and the neural and hamal regions of the body are always completely separated by a partition; the limbs are never more than four in num ber; generally there is a bony axis known as the spine or vertebral column, and a notochord is always present in the em bryo, though it may not persist in adult life. A specialized hmmal system is pres ent in all, and in all but Amphioxus there is a heart with never less than two chambers, and in the higher verte brates with four. The vertebrata are usually divided into five classes: Pisces, Amphibia, Reptilia, Ayes and Mammalia, and many attempts have been made to gather these classes into groups. One plan is to divide them into branchiata (fishes and amphibians), because at some portion of their life they are pro vided with gills, and abranchiata (rep tiles, birds and mammals), having no gills. The latter are sometimes called amniota or allantoidea, because the em bryo is provided with an ammon and an allantois, while both these are absent in the branchiata, which are therefore called anamniota or anallantoidea. Owen
made two sections: Hamatocrya, or cold-blooded vertebrates (fishes, am phibia and reptiles), and Hiumatother ma, or warm-blooded vertebrates (birds and mammals) ; and Huxley three: Ich thyopsida (fishes and amphibia), saurop sida (reptiles and birds), and mammalia. A later classification is to treat all the vertebrata as a division of a larger group, Chordata, distinguished by (1) tempo rary or permanent possession of a rod (the notochord) underlying the central dorsally-placed nervous system; and (2) the temporary or permanent presence of visceral clefts. The Chordata are divided into three groups: (1) cephalochordata, in which the notochord, pointed at the extremities, extends from one end of the body to the other; (2) urochordata, and (3) the true vertebrate, or craniata, in which the anterior end of the central nervous system is enlarged into a brain, and which becomes surrounded and pro tected by a cartilaginous capsule or skull.