vertebrarterial (ver tebrarterial)

Pertaining to a vertebra and an artery: specifically noting a foramen in the side of a cervical vertebra transmitting the vertebral artery. A vertebrarterial foramen is formed by the partial confluence of a rudimentary cervical rib, or pleurapophysis, with the transverse proce proper, or diapophysis, of a cervical vertebra; the series of such foramina constitutes the verte brarterial canal. This structure is one of the distinguish ing characters of a cervical vertebra in man and many other animals. Also vertebro - arterial. See cut under cer vical. Vertebrata (ver-tē-brā'tä), n. pl. [NL., neut. pl. of L. vertebratus, jointed, articulated: see vertebrate.] 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 formal ly recognized in 1788 by Batsch, who united the four Linne an cla es then current ( Mammal i a, Aves, Amphibia, and Pisces) under the German name Knochenthiere; and next in 1797 by Lamarck, who called the same group in French ani maux à vertèbres, and contrasted it with his animaux sans vertèbres, whence the New Latin terms Vertebrata and In vertebrata. But this identical cla ification, with Greek names, is actually as old as Aristotle, whose " Έναιμα (Επεma), or 'blooded' animals, were the vertebrates, divided, moreover, into four cla es exactly corresponding to the modern mammals, birds, reptiles with amphibians, and fishes, and contrasted with " Αναιμα ( Anama ), or 'bloodle ' animals, these being all invertebrates. Vertebrates are the most highly organized metazoans, with permanent distinction of sex, and consequent gamic reproduction without exception. Their e ential 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 cla of vertebrates (A crania), the head has a skull and brain (Craniota). The alimentary canal is completely shut off from the body cavity, 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 slit1, 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 ve els. 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 A crania, 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 endoskeleton and an exoskeleton, the former constituting the main framework of the body, latter inclosing it in space. The Vertebrata have been variously cla ified: (a) pon physiological considerations, into (1) oviparous, ovovi viparous, and viviparous; (2) cold-blooded and warmblooded, or Hæmatocrya and Hæmatotherma; (3) those with nucleated and those with non-nucleated blood-cells, or Pyrenæmat a and Apyrenæmat a. (b) Upon mixed physiological and anatomical grounds, into (1) those with gills and those without them, or Branch i at a and A branch i ata; (2) those without amnion and allantois in the embryo, and those with these embryonic organs, respective ly the An amnion at a or An all an to idea, and the Amnion at a or All an to idea. (c) Upon the most general considerations, mainly structural, Vertebrata have been determined to fall most naturally into three subphyla or supercla es, defined alike by various authors under different names. These are (1) fishes and amphibians together; (2) reptiles proper and birds together: (3) mammals alone. These three brigades have become best known under Huxley's names-(1) Ichthyopsid a, (2) Sauropsida, (3) Mam mali a. They are also called (1) Lyrifera, (2) Quadrat if era, (3) Mallei fer a. The cla es into which vertebrates were long directly divided without brigading were originally four: Pisces, fishes; Amphibia, amphibians and reptiles; Aves, birds; Mammal i a, beasts. Next there were five, by separation of the second of these divisions into the cla es Amphibia and Reptilia proper. Finally, the origi. 6736 nal cla Pisces was dismembered into four cla es: Lep to cardia or Pharyngobranchii or Cirrostomi, the lancelets or a cranial vertebrates alone; Marsipobranch i i or Cyclos tom i, the monorhine vertebrates, or lampreys and hags; Selachii or Elasmobranch i i, the sharks and rays; and Pis ces proper, or ordinary fishes. (See fish 1.) None of the divisions of Amphibia, Reptilia, or Mammal i a are usually accorded the rank of cla es; so that the phylum Vertebrata is now usually taken to consist of the eight cla es above noted. After the discovery by Kowalevsky, in 1866, of the po e ion of a notochord by the embryos of ascidians and by some adults of that group (see urochord, and cut under Appendicular i a ), the Tunic at a, under the name of Urochord a, were added to the Vertebrata, and the larger group thus composed was called Chord at a by Balfour. Later the worm-like organisms of the genus Bal a no glo us were admitted to the same a ociation, and it has been pleura ) may require to be considered in the same con nec supposed that some others (as Cep halo discus and Rhabdo tion. With such extension of the scope of Vertebrata, or rather the merging of that group in a higher one compris ing all the chordate animals which agree in po e ing a (temporary permanent) notochord, a dorsal neural axis, and pharyngeal slits, the arrangement of Chord at a becomes (1) Hem i chorda, the acorn-worms; (2) Uro chorda, the tunicates; (3) Cep halo chorda, the lancelets or a cranial vertebrates; and (4) Vertebrata proper, or ordinary skulled vertebrates.