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Century Dictionary and Cyclopedia

  1. A phylum or prime division of the animal kingdom, containing all those animals which have a backbone or its equivalent; the vertebrates, formerly contrasted with all other animals (Invertebrata), now ranked as one of seven or eight phyla which are severally contrasted with one another. This division was formally recognized in 1788 by Batsch, who united the four Linnean classes then current (Mammalia, A ves, Amphibia, and Pisces) under the German name Knochenthiere; and next in 1797 by Lamarck, who called the same group in French animaux à vertàbres, and contrasted it with his animaux sans verteàbres, whence the New Latin terms Vertebrata and Invertebrata. But this identical classification, with Greeknames, is actually as old as Aristotle, whose “Εναιμα (Enæma), or ‘blooded’ animals, were the vertebrates, divided, moreover, iuto four classes exactly corresponding to the modern mammals, birds, reptiles with amphibians, and fishes, and contrasted with his”Αναιμα (Anæma), or ‘bloodless’ animals, these being all invertebrates. Vertebrates are the most highly organized metazoans, with permanent distinction of sex, and consequent gamic reproduction without exception. Their essential structural character is the presence of an axon from head to tail, dividing the trunk into an upper neural canal or tube containing the main nervous cord, and an under hemal cavity or cavities containing the principal viscera of digestion, respiration, circulation, and reproduction, together with a sympathetic nervous system. Except in the lowest class of vertebrates (Acrania), the head has a skull and brain (Craniota). The alimentary canal is completely shut off from the bodycavity, and open to the exterior at both ends. Special organs of respiration are confined to this canal, and form in the higher vertebrates lungs and in the lower gills, the latter structures being developed in connection with certain visceral clefts (see slit, 5) and arches which are present in embryos of all vertebrates, but which for the most part disappear in those above amphibians. Organs of circulation are present in two main systems—the blood-vascular, consisting of a heart or its equivalent, arteries, veins, and capillaries, and the lymph-vascular, consisting of lymphatic bodies and vessels. These two systems communicate with each other, and the lymphatic with both the mucous and the serous cavities of the body; the blood-vascular system is otherwise closed. The main nervous system is primitively tubular; except in Acrania, it becomes differentiated into a brain and spinal cord, from both of which pairs of nerves ramify in nearly all parts of the body, and effect intricate anastomoses with the sympathetic system. Organs of the special senses are present, with sporadic exceptions, especially of the eye. The organs of reproduction in both sexes are connected with the alimentary canal, except in a few fishes and in all mammals above marsupials. Ova are matured either within or without the body of the female. The embryo or fetus develops from a four-layered germ, whose epiblast is the origin of the cuticle and main nervous axis, whose hypoblast lines the alimentary canal, and whose mesoblast, splitting into somatopleural and splanchnopleural layers, forms a body-cavity and most of the substance of the body. All vertebrates have an endoskele-ton and an exoskeleton, the former constituting the main framework of the body, and the latter inclosing it in space. The Vertebrata have been variously classified: Upon physiological considerations, into oviparous, ovoviviparous, and viviparous; cold-blooded and warmblooded, or Hæmatocrya and Hæmatotherma; those with nucleated and those with non-nucleated blood-cells, or Pyrenæmata and Apyrenæmata.

GNU Webster's 1913

  1. n. (Zoöl.) One of the grand divisions of the animal kingdom, comprising all animals that have a backbone composed of bony or cartilaginous vertebræ, together with Amphioxus in which the backbone is represented by a simple undivided notochord. The Vertebrata always have a dorsal, or neural, cavity above the notochord or backbone, and a ventral, or visceral, cavity below it. The subdivisions or classes of Vertebrata are Mammalia, Aves, Reptilia, Amphibia, Pisces, Marsipobranchia, and Leptocardia.

WordNet 3.0

  1. n. fishes; amphibians; reptiles; birds; mammals.

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